The nut that holds the sensor bulb in place can't be replaced, but the adapter is available at NAPA and elsewhere as a separate part. If yours is bad,just replace it. A little RTV might help, but with a good adapter, the bulb should have a leak-free fit without any sealer.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!