My driver seat in my 1998 Z3 slides a bit when I

Sounds like a track messed up on the seat a loc ore something. Get on your kness and push the seat forward and backward see if you can see where is supose grab underneath.
Tracks are cake work to replace.
See if BMW cover this under this before you have to buy it. BMW stand for buy more warenty my brother law had ZM version it fun little car but not enoght tork for me
If you got get track you find one on junk yard dog.com it normal to just unplug the electic junk it one plug and its 4 bolts take seat out.
i had replace trac on mustang i was try rebuild on 95 Gt it was easy. You could repalce it on weekend in few hours if BMW dosent cover it.
Hope this helps you give thumbs up it does thank

Super common problem in our z3s. I dont think I have ridden in one that doesnt do that. I havent heard of a way to fix it.

needs new bushes, in the track, common problem. email paulhandy@talktalk.net for further info