I reckon these two fellas are spot on,
Silicons aren't the best choise where there is raw fuel as it eats into it. Best is Loctite 515 which is fuel proof.
Another +1 for 515, good gear, and the 518 is high temp.
Cheers Al.
I have balanced and harmonised a couple of scary fast Mercury Formula outboards, just about to do another. Cosworth cast 72deg V6 two stroke block. Metal to metal on the axially split crank cases(Loctite).
Use to hang with boys that burnt the midnight oil preparing Michael Guest's National Evo4 Lancer. They were always Brainstorming for solutions and improvements etc. Transmission always leaking or weeping. Identified cause; shearing/delaminating gaskets because cases were flexing under load. Solution; discard gaskets, run metal to metal joints with loctite 518 instead. No Gaskets = less movement in joint. End of leaks and weeps.
I just pulled apart a Maico reed box last week. It had an air leak. It had several gaskets and metal spacers in it. It had been assembled with Red silicon, which had broke down and failed(from the fuel or oil I was left guessing?). The very next word my mind said when I read Sleepy's first post was "Eureka"