Have you tried taking the hand cleaner GOOP and getting the grease off of the seats?
Our Impala is a light color inside a little darker than off white.
Well after I got it back from having it serviced just by accident I noticed a big gob of grease on the head liner above the drivers door.
I don't know how they managed to get it there, but I didn't see it before I got home. I had already used GOOP to get some grease
out of my off white carpets in the dinning area ( No comment on how it got off of the EAGLE and onto the carpet)
I Just took and put the Goop right on the grease spot and rubbed it in real good.Then I took a clean DRY paper towel and rubbed the spot until I couldn't see anymore grease. Then I took a DAMP wash cloth and rubbed the spot where the grease had been and around it to get the goop off and you can't even tell there has ever been any grease on it. It didn't leave any kind of stain at all. I sure was glad to find out that GOOP works good on stuff other than hands. I noticed it has on the back of the container that it can be used for laundry problems too so I do it.