They already make several great threadlocking compounds. Loctite blue is probably the thing to use; it allows disassembly without breaking things. If the prop valve is in a hot spot, then I would recommend the green compound. It is also now available in a gel, or as a "gluestick" applicator (best idea yet!), which makes for a lot less mess. I am not a big fan of using actual glues, as they might be exposed to chemicals that will react unfavorably with them.