Might try a little;note; a little, Simple Green or 409 on the corner of a shop rag. Also seen on TV, that the Mr.Clean sponge ( the Magic Eraser) is supposed to be safe on most anything.
What ever I used I just try a small area first.
A topic near to my heart and sole of my shoes ! Try as I might and as nimble as I once was, sometimes that heel on the right boot just doesn't make the hurdle. I use " NU Vinyl " now and then for the seat. Looks great when you first put it on, only downside is the rain/ ambient moisture tends to leave black, easily removable , streaks on the side covers. Nothing is perfect.