if you have to really seal an intake to keep it from blowing out you have other issues..... way to much internal pressure. Most of the times I've seen it they vent the breathers too small and when you seal the intake it blows the breather out.
both covers should have open tubes to a catch can.... with good ring seal you should have minimal internal pressure but on boosted apps i set the rings pretty loose because under boost cylinder pressure spikes and rings will pinch shut.
I'll set ring gaps at .0065 x's bore size for boosted apps. looser on the 2nd ring yet.
I use sealant in Caulk gun form.... I do so many LOL I usually use permatex blue or GE blue...
LT1 is a special case, with a totally different intake setup from an SBC. In that case internal pressure doesn't cause it, just dramatic heating/cooling cycles in an oily contact area of two thin pieces of metal. No coolant flows through it so there is no front/rear gasket, and that whole area gets crazy hot if you have emissions since the stock EGR valve is right up against it. A quick search for "LT1 rear intake leak" will give tons of results - many of them probably with replies from me.
Mine leaked twice with standard Permatex, never leaked again when I used "The Right Stuff" . Now that's all I use anywhere that touches oil.