Ok, took my twin 300 bar 7's in for a fill today, afterwards lay them down on the back seat of the car. When i took them out a short time later there was an O ring on the back seat. It measures approx 1.5 cm across. I cant see where it has come from but am concerned that if it did some how come off my cylinders it may be a problem. It may I suppose have come from the filling whip but any ideas ?