There is a NO.2 and and a NO.3 in non-hardening.
I think you be better with a NO.2.
Gasket Sealants : Permatex® Form-A-Gasket® No. 2 Sealant
permatex form a gasket | eBay
Have used both with great success.
My favourite is Ultra Grey.
There is a use for all sealants, as specified by the manufacturer.