My experience as well. The plus side is when you go to paint your seats before you sell the seats take the paint well
. As far as bleach and harsh cleaners go on gel coat it's a losing battle. You're breaking down the protection making it more susceptible to staining, especially the non skid. My new older boat's gelcoat is yellowed and bloody so I just leave it that way. I get it professionally cleaned and buffed to look like new before the summer season starts so my wife is happy to bring her friends on board. Then come late August I'm f***ing it up again.