I got a regulator for my theoben rapid mk2 a couple of days ago.
Yesterday I took the bottle out, installed the regulator and connected the 400 cc bottle back. I noticed a little noise of air escaping from the regulator body and when I sprayed some water around it I found out that air was escaping from the breathing whole of the regulator.
What should I do? Send it back to RAW?
Definitely sounds like a dry, damaged, or poorly sized O ring that separates the high pressure air in the air cylinder from normal atmospheric pressure outside the tube. The purpose of the "breathing hole" in the regulator is needed to determine what psi difference exists between ambient air pressure and compressed air pressure, and O rings are generally the cause of leaks from the high pressure side.
Sometimes some silicone grease will take care of the problem, or the O ring might have moved during installation. Open it up and try again!!