If the Rohm Air Retracts have not been used in some time you will need oil the o rings.
You will need to get some Refrigerant oil , do not used wd 40 or any other oil. Take the time to get the oil.
75 lbs should be enough air. As a test when at pressure the system should hold air 24 hrs. ( down to 45 or 50 lbs)
If you get the pressure to high the sevo will not be able to move the spool.
I have 1000 ' s flight on the retracts. a little care and they work great. You must oil them they were designed to work with r 12.
Would would oil my system twice a year just a few drops.
Good luck Mark