Help freeze plugs and cam plug leaking

OP, how are you installing the freeze plugs? If the force of installing them is concentrated near the center of the plug, it will distort them by pulling in the sides a bit and the fit will not be uniform. They need to be driven in by placing something like a socket in the plug's recess that is just a bit smaller than the pug's recess, and them driving on the socket. That keeps the forces near the plug edges.

And be aware that there are very fine size increments for freeze plugs, like increments of 1/64", which is about a .015" increment. It would be easy to get a size that was .015" or .030" on the small side, and they would install 'snug', but not be properly tight. Where are these freeze plugs coming from? Are they being looked up to be the exact proper size?

As for shellac or Form-a-Gasket #1, they are intended for sealing together tight fitting metal-to-metal surfaces, like sealing together the 2 halves of a piston aircraft engine crankcase for a pressure and oil tight seal.. or freeze plugs. So I am not 100% convinced that is the issue here. But if the holes are pitted or otherwise out of round, then it sounds like the RTV stuff will do you better. Can't hurt to try it next time.