Welcome to the board! I can give you some information, I have a 94 and have collected some info:
Geneeral specs -
http://auto.consumerguide.com/auto/used/reviews/full/index.cfm/id/2117
Issues:
Driveline:
- Water pump will need replacement because of the plastic impeller thru '96 (M50)
- Radiator - look for cracks in the plastic neck
- Defective ignition coils in some of the '91 and '92.
- Drive belt tensioner
- Profile gasket on the earlier 318's (M42)
- cracks in plastic thermostat cover (M50)
- sticking thermostats (M50)
- Manual transmission (ZF model) pops out of 1st or 2nd gear under load
Suspension:
- Outer ball joints go bad
- Rear shock mounts go bad
Interior:
- Window switches
- Door panels seperate because of insufficient glueing
- Dashboard vinyl can seperate over the center vent
- Seat heater elements break
- Glove boxes misaligned - especially earlier models
- chipping trim around the tweeters in the front door panels
- sunroof rattle
Exterior:
- Plastic headlight covers get foggy over time
Misc:
- brake light switch
- squeaky clutch pedal bushing