I'm working on my 98 XK8 seat motors, particularly on the passenger-right because of sluggish fore-aft motion. Removing the seat was fairly easy and after I had it out, the first thing I noticed was how stiff and gummy the old lithium grease was. The movement screws were especially sticky. I hit them with a little penetrating oil to loosen them up, but noticed one side was a little off. Removed the drive motor and the plastic guide sleeves for the drive shafts immediately disintegrated. The suspect side had a bad shaft (picture).

I shouldn't be surprised, the guides are 20 yr old fluted nylon. Parts broke off in the motor housing but no trouble to remove.
If you're pulling seats to clean or repair, it would be a good idea to relube the screws and tracks.
Hope this helps someone from ruining shafts and motors.
tg