Leakage in Hoss air cylinder

Hi, all.

I didn't find any other more suitable sub-forum to put this in... :)

I have made Hoss' 3-stage air cylinder, except I made it a 4-stage cylinder, to use on my WMD25 (same as BF25/G0704), but I have a weird leakage in it. In the normal retracted position, I have a small leakage coming out through the extend line, but when it is operated (extended), I don't have any audible leakage, which baffles me. Instead of using washer gasket or silicone for the air channels (as suggested by Hoss), I made some small pockets and used O-rings to seal between the stages. Other than these two changes, the cylinder is according to Hoss' drawing. Anyone have any ideas where it may leak when it only leaks in the retracted position? In my mind, it ought to leak through the retract line when it is extended since it leaks through the extend line when it is retracted...

I have had problems with the rod seals popping out, but I think they are all properly glued in place now. One thing I can do is to make a new piston rod for only 3 stages and remove 1 stage at a time to see if I can find which stage is leaking.

TIA,
Stig