[Cool Hand Lurker]

On a modern car with synthetic fabric I had good luck with Dawn dish washing liquid in a 5 gallon bucket of water, applied with a sponge to the whole seat so it was all wet. Getting the whole seat wet kept 'rings' from forming when it was dry. I washed out the soap thoroughly with a garden hose on full pressure so it just ran through all the padding and dripped out of the bottom of the seat until it was clear. Then I just let it air dry for a couple of days. Came out clean with no spots or rings.
This whole process was done outside.