I cannot remember the last time I replaced those black rubber seals on the bowls, maybe 8 years. What was interesting is the bowl aluminum or pot metal where the rubber sits was all corroded/ oxidized and the rubber had the oxidation pits on all around it like a chemical reaction. The oxidation took some work to get it off, I block sanded it with 220 on one and used a different one on the back.
I might have used some grease or some sticky gasket sealer when I put them in, but my guess is crappie synthetic rubber and the chemicals in gasoline caused the problem.
I replaced the rubber on both bowls with some I got from Joe a few months ago. Back in the day the rubber for those was red and very rubbery. I still have some old red ones that are kinda wore out, and they fell like rubber still. I see know the black ones I used were junk. I would think they would make them out of that fuel resistant neophrem or whatever it is call. I cannot remember where I got the ones that went bad, but it was not from a SU kit--- but separately purchased from one of the big 3