Problem is that cars were too cheap to begin with, so they were 2nd cars not cared much after, just used and disposed, some elderly drivers bought them too, they still knew how to keep things lasting 40 years, they did live before consumption mayhem, but that starts to be lost knowledge, kids buy these cars use them like stole them and then sell them with low mileage cars that have driven to point they need major restoration.
Manufacturers service program is bare minimum, skipping from that will result problems, to keep car truly in good working order more is needed, just about everything has designed life that it will last 100%, usually bits can last even double from that, but to keep car 100% reliable one must not wait fault to occur to replace things. That is basics of good car care and it does cost a ton.
99% thinks car being reliable when it will go forever with only oil changes, but that in reality is just how well car can take abuse.
Now think about this modern crap made after 95 or so, just wait until those come to age of 300 series, there will be a ton of issues, so much more bits to replace which are all thinner and more fragile, you need to dismantle half of the car to get access to some bits, but everything it attached with use once type of hooks that fail.
For example. for my french crap, I needed to replace windshield wiper relay, Instructions were, remove the dashboard, I took instrument cluster out to find there is solid plastic behind it, so I punched a hole to plastic to gain easy access to all relays. Now big difference with 300 is that you don't need to do such things, there is less parts to take care of, but you need to replace them after certain time or/and after certain mileage, previous owners have not done that, I can say that almost 100% sure, because how society has become and how we are taught use once, dispose buy more new more eco, so old methods of good servicing are forgotten.
I have battery drill from 80's, it still beats most of those attractive packaging versions, it has been taken care of, new brushes, battery, I think that even bearings are done once. Oh yes, you could do that to old ones, forget servicing newer ones. Actually that battery drill was first to appear in market, Fein.
Problem is that attitude we are taught, how new would be better than old, how caring fro old is not 'cool' or whatever, so when we who like from old buy used vehicle it will be crap, it is just some base that is needed to be worked with.
My recipe has been that when I buy car for daily driving, I add at least car's price to first year servicing, up to twice the price of the car might be needed as previous owners might have been skipping servicing, for example my french crap had full book of service records, but I had to replace most of the bushings at front, exhaust, brakes (discs, pads, drums, shoes, handbrake cable, everything) oil was thick, oil filter was rusty, air filter was so thick of soot that it had 2mm thick layer of it on side were air enters to filter, some bearings have needed replacing and there are lot of things that have not been working, like heater fan and windshield wiper except fast speeds, it still has some I have decided not to fix, like headlamp washers, radiator e-fan, central locking etc. Have had rust holes, sills needed to be made from scratch, starter motor failed, even alternator belt failed and I did bring it to garage so they can replace that at 6 months before it failed, so that tells something about quality of servicing when you buy servicing from some garage.
So only way to know state of the car is to work by yourself with it and do everything during first year of ownership, replace everything that in theory can fail.
After that comes rust proofing, which can take even more money in old car, there will be welding even in spotless car, there is always some place, full underside cleaning would be needed, underseal and all that after that.
Only after then car is in known state and can be started to cared after to keep that good state of car, but this all cost a lot and takes lot of time, also workplace and tools, so it is quite difficult to make happen, but that is only way to get car to shape it was originally and to know if car is truly reliable or not by design and by model.
32 year old car that was last one I bought will require quite a bit of work to become good one, there are so many things wrong with it still, but eventually I think that it will be done by this principle and I can say it is in good condition.
Then there is modifying and abusing of vehicle (using it in motorsports), car was designed to be shopping car for families, more or less, it was designed to have 1.4l motor and CVT transmission, never it was designed to be cornered on race track or driven at autobahns with gazillion mph.
That means that car needs to be modified, factory did some modifications to make 2ltr motors usable in car, but despite their efforts there are bits that are not too strong, so to make car take something as stressing as drifting without failing, you would need to change whole lot of things, from engine mounts, to suspension arms, rear axles, gearbox and differential are no good either, even they might last some time, they really are not such that would last long in such stressing conditions, driveshafts and their joints are also way too weak, even body need to be made stronger.
Point is to make car do things it was not designed to do, you need to redesign the car to new task, which needs then replacing most of bits there is and making body stronger, or else things will fail.
There is reason why racing parts are made, they are lot stronger than standard parts, even with BMW 300 series which is made for more power to begin with, there are bits that fail unless made to withstand actual realizing of that power for such as drifting or rallying.
Every mounting should be made a lot stronger is thing to begin with.
Again it will cost a lot, but when you look those cars that are actually redesigned for motorsport use, there is high price tag with them and they still will fail, just not so often and it will take quite bit more to make them fail.
Disappointment comes from faulty assumption most of the time, realizing assumption has been faulty generates chance to find new ways to make hoped characteristics possible. There are several routes, easiest might be selling the car and getting something biased more towards motorsports to begin with, but as has been said that is easy boring way, well not very easy and certainly not much cheaper either + settling back with average status with no chance to be different. One could also sit back and look whole picture, what has been done, what has been failing, what there is left to fail and then just start planning budget that would make car to be what one assumed in first place.
Any project should be started with planning budget and staying with the budget, without that it just ends badly for the car and for the enthusiasts.
Problem is that we live on illusion created by our minds + marketing and are not taught how to face reality, so it is easy to underestimate costs and overestimate rest.
This is at least what I have gathered from things during the tens of years, but most of these are just my minds illusions naturally, which might differ from your illusions, but for individual their own illusions are true until bubble is burst
just need air conditioning, stereo/antenna to be fixed (only get static :S), new fog light & front dint pulled out.