I don't have one here handy to compare, but I believe the servo diaphragms should be airtight and hold a vacuum.

I think if yours won't hold, it's probably got a hole (probably age crack) in the diaphragm.

Might be off topic but, can issues/leaks with this system cause a higher idle at idle? When pull to a stop after driving around the idle is noticeably higher (1-200rpm), if i give the throttle a blip, the idle returns to normal. I've changed out the return springs thinking that was related but no change.

Doubtful unless the linkage to the throttle opener system is binding up or something.

Next time your idle hangs up, pop the hood and start pushing on different places on the linkage(s) and see if you can figure out where it's hanging.