OK, finally the thing started to leak fast enough that I could track it. I pulled off all the shrouds forward of the trigger assy. to reveal the bottle and regulator. There are two screws that are very well hidden in the rear most shroud that took me a while to find...sneaky Umarex. Air was leaking out between the two halves of the regulator. The Gold colored half is glued to the bottle and un-removable, but the black half of the reg is what contains the belleville washer assy's. At the forward end of this assy is a teflon oring, it was the culprit. It was leaking and allowing air to flow back out between the two halves of the regulator. I replaced the oring and reassembled. It's now been holding a full charge of air for 24 hours...yay!
Chris