... my 45 gallon aluminum tank has an aluminum inspection lid about 8" in diameter, there are 8 machine screws tapped into the tank that fasten it, so the hole is maybe 7" in diameter. This fall I want to clean the tank. The gasket that is in there now should be replaced it could be 25 years old, it is thick maybe 3/16" black neoprene or rubber, it could be 1/4". Wondering the best method to gasket this inspection lid would be ... should I use neoprene again, if so what type and how thick ? Or should I go to something like a LocTite product, like their 545 (but I think this is a thread sealant) ... or a Permatex RTV or which one ?

The fasteners are about 2" apart. Is that too much, should I add another in between all the way around ? I don't take the inspection lid off but maybe every 3-4 years for tank cleaning.

Thanks, cheers, John