The shop vac idea is great - I have used that in past for greasy clothing (spraying brake cleaner on one side of the shirt with the shop vac sucking on the other), but didn't think of it for this. Woolite is another good idea - might be less harsh than Tide. These seats have been rained on a bit, so I suspect one more dousing with water won't really hurt them. I can always remove the upholstery if this isn't enough.
Colo Springs, CO