At 02:40 PM 7/1/2010 Thursday, Mike \"Rocket J Squirrel\" wrote:
>The cap is a three-part construction: two plastic cap parts, and an
>elastomer ring captured between the two pieces. This latter provides a
>seat for the lip of the tank drain outlet. The ring seems a bit mooshed.

Vaseline the spout.  Carefully lay some RTV gasket compound over the
existing rubber, let it set mostly and then screw it on the spout,
not too hard.

I've done this with other similar things, not this particular one.

Yours,
David