The first patch of bad rust has been discovered on my 340!!!
Well, ok, it's not that bad, but its the first bit I've found that isn't surface, this has gone through the panel. Luckily though it looks really easy (relative I guess) to put a plate in. It's on the corner, by the headlamp, passenger side, just where the crossmember that the headlights and radiator hang on attaches.
If you havn't checked there (I'm not sure how common it is), might be worth a look. The fact the the tyre well is there gives plenty of working room.