Getting oil out of cloth seats

Removing the cover is a given. I would presoak it for a day or so in just enough warm (not hot) water to completely cover it, with two full measures of a good brand of liquid laundry detergent. Then I'd run it through a good washing machine, but only if I had the front-loading kind -- the top-load kind with an agitator would likely screw up the cover; if that's what I had I'd take the cover directly to the cleaners and have them dry-clean it. Maybe I'd save myself the hassle and just do that as the first step anyhow.

The foam's likely going to need replaced; you will have a VERY difficult time getting all the oil out of it and it will soak into the cloth cover again. If you can get most of it out, put an oilproof liner layer between the foam and the cover when you or your upholstery shop reassembles the seat.