If you don't mind spending the money, order this:
Amazon.com: McCulloch MC-1275 Heavy-Duty Steam Cleaner: Home & Kitchen
I bought one about a year ago after one of my car buddies let me use his. Seriously one of the best investments I've made. No doubt it will clean your seat. Great for interiors. Does wonders on wheels, interior, vents, etc.... If you shop around you can get it for a bit cheaper (I think I paid $80 shipped).