Interesting reading about the retract air problems. My experience was totally different. At least a half dozen different planes over 10+ years and only once did an air retract not deploy. My fault because I forgot to check for leaks in the up position. Mostly Robart valves, but a couple of others also. Sierra, CJ, Robart retracts. Mostly Robart tubing and plastic tees. I put 10 -15 drops of oil in the air system a couple of times a year.
To check for leak I put air line extensions between the wing and fuse so I could watch the oil move in the lines. The oil heads right for the leak. May have to add a few extra drops of oil. Use forceps to block off different sections of line to zero in on the leak.
Brian