Hi Max,
Just in reference to the silicone not standing up to the fuel, I have used it for about 30 years on bolting carbies to manifolds on cars and I use it on the pull start seal on the PT's and on the inlet manifolds if I ever need to change one and so far I can't recall ever having an issue with the fuel causing me problems so I can only go on personal experience. In Alans case here who cares if the seal started to fail in years to come, it is only a 15 min job to pull the barrel, split the cases and reseal if ever needed which I would be amazed if the silicone didn't hold.
