After changing my clutch and cleaning years of grime off the clutch housing I noitced that I've got a nice slow leak out the back of the engine which drips onto it, I wouldn't mind so much but some bright spark put a hole at the top of that housing for a sensor so oil and dirt can happliy get in and I don't want an oily clutch and to have to change it ever again.

Since theres dozens of pipes out at the back of this engine (1.7gl 1987 btw) and I don't know why... seems to be more complicated that needed but thats besides the point, I have no idea where it is coming from, is there a common inlet/outlet on the back of the engine that tends to spring a leak? Where can I get a full set of hoses for the back of the engine to replace them all so that I can rule them out?

Any help greatly appreciated, also the road will look a lot cleaner where I park my car

There shouldn't be any pipes with oil in (except for the breather pipe to the air filter). It might be a badly sealing/overtightened rocker cover?