Man, I used to think any sealant labeled for fuel was fine. Seeing murphy.emery's story about the gooey mess changed my mind for good. The right rubber part is the only way to go.
Yeah, the phrase "wrong sealant" might be the issue. Most fuel pumps need the proper rubber gasket or O-ring, not a liquid sealant. That stuff can actually get eaten away by fuel and cause leaks. You gotta use the specific part meant for it.
Totally, I learned that the hard way on an old carburetor. Used some generic gasket maker that swore it was fuel resistant. Two weeks later it was all soft and gooey, weeping gas. Swapped it for a proper nitrile O-ring, the exact one from the rebuild kit, and it's been bone dry for years now. That liquid stuff just can't handle it long term.