I use Threebond 1104 on my gearboxes. It's a bit of a favourite of mine from my motorcycle engine builds. It's much more adhesive than silicone and doesn't have the tendancy for
oil to work its way between the seal and the metal. I use it for sealing crank cases together on bikes and these generally have no gaskets, just the machined faces. on old engines the case halves can warp a bit but this stuff still keeps them sealed.
Here's a link:
Threebond
Cheers