To be clear, that is spray silicone that is being suggested. I had a truck where the previous owner used a tube of silicone to seal the rubber filler neck. Every time i put gas in, it would dissolve some of the silicone, only to re harden somewhere else in the fuel system. Nothing fixed it except to rip out the entire fuel system, and replace it.
That's right. There is no "silicone" based sealant or gasket maker that can withstand constant exposure to gasoline or gasoline vapors. You shouldn't need any sealant on the filler tube grommet anyways.
