I've used Hylomar to aid gasket installation (hold o-rings, lube seal OD's, etc..) for many years with great success, especially on vintage machines with mating surfaces that were considerably less than perfect. An added benny, since it's a gasket dressing and not a sealer per se, is that you'll never have to scrape another gasket once you start using it as the gaskets will just peel right off later.
Another trick on the old stuff is to prep the mating surfaces by stoning them. Lube the stone with a little bit of brake fluid and then go very lightly in a tight circular pattern. Clean up the surface with a little gas on a rag and you're done. Often times the weep/leak is caused by a scratch which runs from the inside to the outside of the surface. But if you get a really gouged surface, one where some butcher pryed it open with a screwdriver, well, yamabond and and a piece of clear fishing line to fill the divot may be the only help until it can be welded and milled.
Hylomar is sold in most auto parts houses and in a non-shop environment a tube of blue will last quite a long time.
http://www.hylomar-usa.com/
Silicone goop is never a good option to seal anything that oil moves through. As the mating halves are drawn together the silicone will squish out and bead. What you see on the outside is happening on the inside too. The last thing a guy wants is to take a chance on a cured and hardened piece of silicone moving through oil galleys in his motor.
