cassette player keeps switching sides
 

I still have the original factory head unit in my 92 325is. The cassette player keeps switching from side one to side two.

Any ideas on how to correct this problem short of removal/replacement?

Oh, what is that wear problem called... something like "capstan tension malfunction"... I can't remember. Anyhow, the problem is that the tensioner that drives the tape has weakened, and the amount of drag it sees is now triggering the auto flip feature of the deck. Now, it could also be that the deck is working fine, but your tape has too much drag in it and that is what is triggering the auto flip. Does it do it on all the tapes you have? If it does, then replacement is probably going to be cheaper than repair.

It does this when I have the adapter running through it (so that I can use my portable cd player). I will try a real cassette to check it out.

Oh, if it runs with the adapter, then it is definitely the player itself. Hmm, before saying things are worn, things are more likely to be dirty. One doesn't want to 'blow out' electronics components because of static discharge, but you can try getting into the drive from the cassette door with a long handled Q-tip and cleaning the system (with Isopropanol), then adding a little silicone lube in the drive system (don't get it on the tape head though). Don't use WD-40 because it tends to dry out quickly. A silicone lube has more staying power. Good luck.

Do you think usiing the "official" bmw tape cleaning system might work? I think I have it stashed somewhere.

Yep... a cleaning tape should help.

Do you guys know anything about my CD player skipping in a 1999 328iC

I have no idea.

I don't think that auto-reverse malfunction via the adapter is solely a problem with your unit, or any other E36 unit for that matter. I had the same problem with my Volvo 760 turbo when using the tape adapter. I think these factory units get 'confused' when there is the presence of another head as opposed to movable tape. Cleaning the unit head & the adapter head always worked for mine.

Depends on how it is skipping. The predominant reason for skipping is that the rubber hub which the CD 'floats' on has dried or hardened up... it causes the CD to move out of alignment and therefore allows for skipping. This usually happens to older equipment, but with having a 1999, this shouldn't be your problem... other than just the cold weather causing the system to be a little more sensitive than usual.

Can you describe the skipping? Meaning, is it a sporadic... or constant... or different between CDs? Is your system just really sensitive to any outside vibration? More clarification can help pinpoint the problem area.