Hi KeithJ, I use the Loctite 518 variant. I tried a "no gasket" approach on the primary cases as that gasket is a pain to make and it seemed I would be forever finding reasons to remove the cover
but it leaked badly without a gasket so I went back to using the thin gasket approach.
Just a theory but using a gasket effectively means you get 2 thicknesses of gasket goo, so more chances of sealing a gap?
On my primary case I can fit a 10 tho feeler guage between screw holes so there is a fair gap to fill, due to the cases being distorted.
I have tried using thin (ish) gaskets with just grease. then Loctite 518 one side and grease the other so the (thin) gaskets would come off cleanly and could be re-used, but I got leaks, so for me I have to comprehensively clean gaskets faces and use new gaskets and the loctite both sides....every time.
I've not gone as far as using a glass plate and wet and dry paper to flatten gasket surfaces, as I have found what works for me to stop leaks. When rebuilding my engine I did carefully file the cases where needed, around the bolt holes, to remove the "obvious" raised areas, just to reduce the gaps a bit.
At least the Loctite is fairly easy to remove compared to some sealants, and as far as I can tell it does not have the same tendency to clog oil ways as silicon, at least I've never found any on the various gauze filters.