Our '98 1.9 just received its 9th oil change (7 by me, 2 under wty), at ~22K mi, within 10 months...
...///MZ3.Net's FAQ is helpful (link provide below). I'd like to augment the FAQ with the following:
The FAQ mentions having a sharp tool for o-ring removal. I posit that a SAFETY PIN is ideal for the task. Just put sharp end under o-rings and yank off. What's really nice about using a safety pin is that you can close it; and, thereby, not worry about o-rings possibly flying around and ending up in places they don't belong. Tidier too.
II. OIL FILTER CAP WRENCH:
I used the wrench made by German tool maker, Hazet, for the first time during this last oil change. (Hazet 2169; BMW# 88-88-6-114-650; $13.76 list, $11.01 w/ BMWCCA discount.) Made of aluminum, with business end & female boss (for 3/8" extension) being much deeper than the generic products. Very nice; makes torquing to 25 N-m a breeze. It's well worth it, imho. Looks kinda cheap, tho.
BTW, I posted inquiries regarding this tool twice prior to purchase, but no responses. I was disappointed with the FloTool #7 ($3.99) generic version. However, one other person felt it was adequate.