SO this is the new seal on the connector. Half an hour later (applying the "Insanity-method") I successfully put the connector back on (again with my left hand). According to Albert Einstein, trying the same thing over and over again and expecting a different result is the definition of insanity... Well, the connector just did not want to go back on - and the rteason was not the new gasket, because just to test it, I tried also without gasket: I do not know why, but it did not want to go back on