Just replace it with a pipe plug.
What could go wrong?
LEGAL DISCLAIMER:
iffn anyone out there is dumb enuff to do that, darwin is on his way
Serial, if the new one leaks it's either defective or maybe it got twisted, warped, er bent during install.
Did you try to pop it and let it re-seat? Sometimes that works.
Good teflon pipe dope can almost seal one of these when hand-tight. You don't have to crank down that hard.
HTH