I searched for an answer on how to do this, and could not find one. Now that I have done it myself I thought that I would post the results. I never read the "appearance" forum, so if this is old news then at least it is available in the search archives.

I had some bad stains on my cloth seats (94 Z28, graphite interior) that I thought would require new seats. One seat had an ink stain from a leaking printer. There was also a large brown stain of 1 square foot or more. I don't know if it was spilled oil of some kind or coolant, or what. The car had been stored for 2 years, so I forget.

Anyway, I removed both seats and realized that the cloth covers come off pretty easily. I washed them in a machine washer using liquid detergent with cold water, and set them out to dry. They looked new, and they smelled like a clean white t-shirt.

The only difference I could see once the covers were back on the seat was that a small amount of elasticity was gone, but this is only noticable from below where you stretch them back over the frame.

New covers are very expensive, and used seats are probably not any better than what you have. So, if you don't mind spending a weekend (remove, wash, air dry, assemble, and install) then you will find out if your stains are as bad as you think they are. Mine weren't.