[JayChicago]

I once called Permatex tech support to ask that exact question. Was told Blue is unaffected by gasoline, can be used in the presence of gas.

But I'm still wondering why the gasket is not doing its job? If you use sealing compound, what problem in the future getting the sender off, possibly pieces of gasket/sealant getting into the tank? I don't know if you should use a sealant. Let's see what others have to say.

Edit: After reading Kube's response above, I would trust his deep experience over what I was told by the Permatex help desk.