John, in our neck of the woods (IV Corp) scuttlebutt was a dry transmission was good for either 30 or 60 minutes in the Huey, forget which. Reputedly from a Bell rep. Had occasion to try it out (no pressure) when the filter O ring let go and flew for some period to get to a FSB (<15 minutes, memory as to how long not that good). Occurred during the Cambodia push when spares were impossible to get, hence maintenance reuse of O ring during filter change. Maintenance arrived and I refused to fly it home, they topped it up and flew home. Can tell you a T-53 will run for long enough to take off and get you out of trouble with no oil as well.