In retrospect, I wondered why the cap didn't have a safety chain so it couldn't go more than a few inches from the filler port.
They used to have! The problem was that the caps often got left off and then would stay attached to the chain for a while until they came off in flight.
Removing the chain means that hopefully the cap will fall off before you get airborne. I always place the cap on the pilot's seat during refuelling.
Back to the original question, check that there are no marks on the cabin roof just under the rotor mast fairing. These would indicate that there has been mast-bumping. Also worth checking is that there is no trace of oil on the inside of the MRGB access door. This would be an indication that the sprag-clutch seal is leaking. Checking that the OAT gauge and the CAT gauge match (first flight of the day only) is always worthwhile.