If its the hole I think you are looking at, very prominent in the photo, that is the air pressure inlet for pushing the piston up and retracting the gear. But it could be used for both, assembly and for air inlet.
I'll have to get a magnifying glass and really examine the seal and see what's what. If I can't resolve it, even though it works perfectly, it's junk if it can't hold pressure for a full flight.
In the gear down configuration, the air system only lost about 3 psi over a couple hours when pressurized to 80psi. In the gear up, well, from 80psi to 0 in about 15 minutes.
