V6 Rocker Cover Gaskets

[Fylnn]

I just changed the gaskets on the rocker covers of my GTV6.  Old ones were getting a bit old.  But new ones leak.  I had them torqued down good and tight with respect to the threads in the alloy.  I would assume they should not have sealant applied since then they won't come off again without possibly damaging the gasket.  Any tips on effective sealing of these things?