I took mine apart and found ton of gunk inside, as you have. I can’t see a slosh sealer working with all that crud from the original seal in there.
Upon advice of another member on this forum, I resealed it with an aircraft tank sealer, figuring if it was good enough for airplanes, it must be good enough for an outboard. He was right, it worked great.
I’ll have to search and find the info for the product. Be back inn a few………
