I've never had a low pressure issue with my air-o-matic. After I saw this thread, I timed mine and it takes 3 minutes to reach 120 psi. I have been through my air system and it has no detectable leaks. Will hold pressure for at least a week although after that time it's down close to zero.
To the OP, do you have the regulator installed by the frame near the wheel? If so take it out- it is not needed on the M35. You will need a couple of plumbing parts to reconnect the hoses, but easy to find. Also make sure the air is turned up all the way at the valve mounted on the firewall. Try checking the air-o-matic system for leaks while someone else is turning the wheels. It should vent air while changing direction but shouldn't leak anywhere else.