there are lots of things to check out, i dont know how much you can do as a visual check, but if he allows you to take it to a mechanic's you might be able to get a full just of whats going on..
as for things to check.. i would of course review this comon fault list. lots of the common issues on e36s will be a good place to check..
here are some that i copied/pasted
-Sub frame failure(usually only the 92 and 93 models)
-ignition coils cracking M50 (usually only 92)
-lifter noise M50
-rear shock mounts
-irregular idle
-water pumps from plastic impellers to metal
-window motors
-tranny mounts
-Differential Clutch Pack Retaining Ring Bolts Backing Out
-ABS light goes on
-thermostat housing cracks and thermostat (M50)
-radiator, look for cracks in plastic neck
-Profile gasket on the earlier 318's (M42)
- Outer ball joints go bad
- Rear shock mounts go bad
- Seat heater elements break
- Glove boxes misaligned
- chipping trim around the tweeters in the front door panels
- Plastic headlight covers get foggy over time
- blistering door panels
- leaking or sticky VANOS unit
-rear toe in bushings
-broken fog light
-control arm and bushings
-taillight failure
-steering fluid bottle leaks from bottom at return
here is an article on common issues
