I have been working on VW's exclusively since I was 16. Mostly aircooled but now that I'm older I like the luxury of watercooled(heat and AC). I have worked in the repair business, and have been in the aftermarket parts business for the last 4 yrs.
I have come to the conclusion, that the only way to go in regards to parts is OEM. Sure an aftermarket air filter is no big deal but otherwise 95% of the time you will be much happier going with OEM parts. If you shop online you will actually find OEM parts cheaper than if you were to walk in to your FLAPS. I am being honest. Sure, you have to wait for mail order, but it is better than having to do a cv axle job 2x or r&r a radiator twice due to inferior materials.
There are a few aftermarket companies that are top notch, Fel-Pro and Timken to name a few. But mostly the aftermaket produces a part that does not have the exact fit or reliability as OEM. How does it feel to spend 2 hours(first timer) to remove a water pump to find out the replacement you bought at your FLAPS just doesn't fit exactly right. So you wind up having to "make it work." If you do the water pump, then a radiator, then a cooling fan motor, and you have to rig each of them to make do, are you really proud of your car any more?
I still am employed full time in the commercial aftermarket business because I enjoy the people, but choose to put genuine OEM parts on my VW's.
P-mail me for suggestions to good online vendors.
Paul '82 Vanagon '89 Jetta