Today I decided to check the health of my spark plugs, as it's been a long while since they were replaced. 5 of the 6 spark plug wires come off and go back on easily, but the last wire simply will not click back into place. Every time I push it on, it "unclicks" itself. I don't want to run on only 5 cylinders! How can I get this last wire to go back on the spark plug?