non-hardening sealer for body nuts

Butyl rope would work good but damn it can be messy. You could even use "duct seal" available at hardware store. Its used to seal air conditioning systems. Its real cheap too, about 5 bucks for a block of it.
https://www.menards.com/main/electr...t-sealing-compound/ds-110/p-1444430996940.htm