Had my s400 about a week, only shot it twice, needed to refill as it was down to 100bar, connected my bottle, started to fill slowly. At about 150bar, I get a squeaking/ squealing noise, and it won't fill any higher. I had the connector on firmly and rotated 90 degrees to lock it. Held it while filling, loosely so as to not put pressure on it. What am I missing? O ring grease?