My two cents about the Aeolian screw-in valves:  If they are hard to
remove and replace they are probably warped.  Brass is a soft metal but
does not corrode in a way to rust them shut as others do.

You may want to check to see if the seal is tight on the valve.  Clean
both surfaces and try again.  Mine screwed in tightly but smoothly.

Eli Shahar