Check valve it is.
Determine due to lack of external leaks. It was leaking back upstream. Thanks for the tips.
Sorry. This post was supposed to go onto the end of my air question.
FWIW found a complete check valve on E bay for 16$,
52 $ for the same at NAPA.
and the repair kit at" find it parts". We'll see if it is correct . RN10y Haldex