I watched videos on using the Dupray steamer (by Mike Phillips) and the car seats looked brand new after they were cleaned with the dry steam in this unit..no, I don't have one yet but I plan on buying one based upon the videos and information I have read about this steamer. I am sure there are other steamers too that can also do this job proficiently. Maybe a friend has a steamer you could borrow to use on the seats.
This is posted in another thread on this site. See how this member cleaned up a Jeep Compass vehicle and what he used to do this.
I don't have a steamer but I do have the tornador black. I was thinking an APC and soft brush then the tornador. Don't wanna much too much water in them thou.