I soaked mine with silicon spray. Then I tool a piece of 1/8" flat bar and ground a slot in it that would span the throat of the plastic screw in piece. Stuck it in the slots on the plstic piece and unscrewed it
Used the same tool to reinstall it. Applied plumbers grease on the threads first so it will come off easier in the future.
-"You want to make it two inches - or, if you're working in centimeters, make sure it's enough centimeters for two inches."-Red Green