Some time ago my check engine light came on intermittently. My gas cap appeared to be in good shape, except that the rubber washer was quite hard but not cracked. I bought a new washer from the MB dealer, but it did not fix the check engine light. I also noticed when I unscrewed the cap there was no sound of the vacuum being released, and I found gas in the flange below the gas cap. I tried replacing the gas cap, but the light stayed on, I got no vacuum and the gas continued to collect in the flange below the gas cap. I tried replacing the gas cap with one from Blau, but same results. For some reason I just can't get a gas cap to seal my fuel tank and I don't understand why. Is this a common problem? Any suggestions for what I can do to get a proper seal for my fuel tank?