I use RTV Black - haven't used Blue in years. I just don't like the way it's worked for me... Could just be me.
In extreme cases, the usage of LocTite #518 Gasket Eliminator is indicated, and it works well with or without a gasket (but better if it has a gasket to bolster it.) I've used this stuff to seal up transmissions I've rebuilt on CASE Forklifts, just because the gaskets couldn't be had, and it's still working just fine.
Still, Black is good for general use.
5-90