This subject goes on forever, but I came to use 3 Bond 1184 on a 1966 Triumph TR6C rebuild that won the Africa International Concours overall in 2018 with only one very small weep on the entire bike ( this is pretty tough to achieve IMO) and now intend trying it on notorious things like my A7SS rocker boxes.
Having observed with envy for decades the Japanese bikes oil-tightness, I've tried this Japanese product used by the top auto/motorbike manufacturers and it's brilliant, no wonder used by many OEMs. It's gooey, sticky,thready and tacky to apply, you have to work fast and get a even coating of about 0.5mm. The only thing I know that thins it, and I keep handy, is a thimble of Acrylic thinners to dip my finger in for smoothing out.
I always leave time for it to dry out a bit and use various torquing and mating methods which I won';t bore you with if not asked.
Anyone else tried this stuff? I have found it for most applications very superior to silicone and others for most applications. But these need to be carefully chosen and applied. Nor is it very cheap and cheerful, but I think well worth the few quid for the numerous places it can be applied. For crankcase halves, barrel-to-block and others IMO it's tough to beat.