I've had virtually no problems with the engine, besides regular maintenance (oil changes, plugs/wires/distributor cap/rotor, air filter, etc.) A previous owner was a mechanic and had rebuilt a majority of the engine, which is probably the reason for the lack of engine trouble on such an old car. The problems, which are typical of VW's, were small things.
About three months ago my drivers side external doorhandle stopped working.
The heater fan switch stopped working and when I replaced it the fan still wouldn't work, even after replacing the fuse. I have yet to find the cause of the problem, but I think the resistors may be blown.
The driver's side door sags a bit, causing a leak during large storms and lots of air noise on the freeway.
The window rollers feel a bit 'sandy' and are hard to turn because of wear.
The trunk cover is warped because it is made out of thin wood.
The sunvisor hooks were old and one snapped off.
My brake light sensor shorted out and burned a hole in the brake line. The funny thing about it was the burned hole leaked brake fluid, which helped me locate where the problem was. I found the sensor and replaced in 10 minutes for 10 dollars.
There's slight electrical problems causing the dash lights to flicker when the car has been running a long time.
Most of these problems have just been related to the age of the car. Other problems were not related to quality problems. E-brake shaft was bent by a mechanic (!) who pulled it too hard while doing a smog check and there's a crack across the windsheild which is getting worse every year. The car was also in an accident some time ago, but the structural integrity of the car is still intact.