Does the PCV grommet fit tight on your cars? I'm surprised it seems to just sit in the back of the intake. Maybe the PCV itself once installed makes the grommet fit better? I guess I could put a little RTV around it.
It's hit or miss. Sometimes the hole is intake is a little off, sometimes it's the grommet itself that's a little off.
RTV will work if you clean port and grommet thoroughly. It needs to be high temp and it needs to be oil and gas resistant. "The Right Stuff" from Permatex works very well for nearly any kind of sealing under the hood.
I ordered a Ford breather filter. grommet and PVC valve from a well known Mustang specialist. The new grommet was looser than the old, rock hard one! I have it wrapped in PTFE tape for now, but a new grommet with sealer sounds better.