I've been using this since the late 60s, has never failed me. Easy cleanup with denatured alcohol and is still pliable and easily removed 50 years later.
Permatex 80019 Aviation Form-A-Gasket No. 3 Sealant
Before the attack: No, it's not FAA approved, it's a US MilSpec approval and it's designed for the machined join surfaces in engines.