Some info on 33s per the original post.

They are old enough now that they all rust. Series IIs are getting a bit harder to find, and most will have had some rust repairs done unless they live in a very rain free and mild winter climate. Series IIIs rust as well. The late ones were galvanized, but it was not great (not like todays manufacturing processes) so damp still gets into the welded seams.

Places to look for are:
- Around the fuel filler area on the rear quarter - Fairly complex to repair, and if the inner skin has gone, will need attention
- Rear sills and jacking points
- Front jacking points
- A posts
- Inner wing to bulkhead seam
- Middle seam across the floor behind the front seats
- Boot floor is boot seal gone and water getting in

And everywhere else, but the above are the major areas.

Suspension wise, fairly straight forward and easy to service and replace, so no worries there. Bushes wear but are all replacable and powerflex do urethane bushes.

Brakes wise, front discs are very small. Smaller engine models got solid brakes so best to make sure they are vented. Well maintained brakes work OK, but there are size upgrades if needed. If on the continent, try and get a very late series III with rear discs (only fitted to the P4 otherwise).

Electrics are unfairly criticized. They seem fairly robust and no worse generally than other makes of car for that era.

Engines - fairly strong. As long as regular oil changes and cambelts, should be OK.

Gearbox - if you are buying, test drive it and get the box and engine nice and warm. The shift is very rubbery, and you need to make sure you are right over for first and second. Synchros get tired, but I reckon this is mainly because of lazy gearshifts working against the rubbery mechanism. Linkages wear, particularly the one to the selector rod on the box.

There are a range of interiors. Late cars had re-designed switch gear, and alcantara Recaro seats. Top of the range 16v had these or fabric Recaros as did the P4. Handles and other fittings are cheap plastic, and sometimes crack with age.

Sport wagons are generally rarer, and P4s are the permanent 4 wheel drive version. On P4s, look out for the viscous coupling and bearings being past the end of their life, and the control electronics being unreliable, but otherwise a fairly robust system. All P4s judder a little at low speed on full steering lock as the VCU detects a difference between wheel speeds and locks into all wheel drive.

Hope this is helpful. Let me know if any specific questions. There are relatively rust free ones out there (I have 2 series IIIs with very few rust problems, one with some cosmetic issues, a series II which is good apart from the filler area, and a P4 which is very rusty).