The measured way of checking is to cap the PCV inlet on intake, remove the large hose that goes to air filter housing. Put a pressure gauge on that large hose. When you start the engine and plug the open hose end of the PCV line with your finger, you should be seeing a gradual rise in pressure as pressure builds in crankcase. If you have a vacuum then the gasket is leaking. Dont buid more then a couple of psi pressure while testing else you could cause gasket damage from that.
In place of a gauge you can use the feel of your hand, takes two people. Did that when spot checking a used truck for my buddy. And it was leaking....