.20 Cal Sheridan Blue streak (1974)resealed and new pump cup and still won’t pump up!

Are you cocking the rifle before pumping ? If not that might help it to seal.

Yes

6 min 20 sec mark

Adrian, you haven't mentioned whether you're able to build pressure but it leaks out fast, or whether no pressure is created. A few notes:
> If you feel no resistance when pumping, something is not right with the pump cup.
> If you feel resistance but the pump handle is forced all the way open after pumping, it's a check valve issue.
> If you hear air hissing out the barrel, it's an exhaust valve issue.
> The original valve body is fine, assuming you cleaned it up for re-use.
One item sometimes overlooked, is the need to polish both the brass intake and exhaust valve seats. Any nick on their surface can cause leakage. Emery paper on the end of a dowel will work for the inlet seat far down inside the innards.

Tell us more about your specific symptoms, which can lead to ideas for diagnoses.

Don R.