Is there room for a rubber expansion plug? They're simple to install if you have enough depth behind the plug for the rubber and the washer to fit properly. Then just tighten the nut until the plug seals the opening.
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!