Those ideas above mine...solid. Both will work. I'm a detailer. So, step 1: remove seat before polish or wax. Lol! I always clean the surfaces with 70% or higher ISO alcohol mixed 50/50 with water. It will work on the seat as well with a little agitation. Try not to scrub.
Dawn dish soap should do the job as well. Might take a little more agitation than IPA but it will work.
Steam is always a best friend but not everyone has a steamer. I don't recommend trying to use steam from an iron at two inches from surface. Asking for problems there.