The pump loses prime after about 20 mins or so. What does it do? stop pumpi9ng water and ill with air?
It looks like it may have been a DE filter at one time Why do you say that?
and I just had a tech out yesterday to replace the valve for the return jets. What valve did he replace? Got a pic?
It's leaking air at the filter head. Actually, pump running, it should be leaking water, not air, if it's at the filter.
When the pump is turned on the lid pops up a little. It should draw down, not pop up. Does it stay up?
Also the pressure gauge does not work. That's an easy one....replace the gauge. It is important to get that fixed if you intend to work on your other issues.