Dear Dale:
You might try heating up the metal around the whole, which in turn will
heat the rubber and hopefully, you will get a softer rubber plug which will
yield to your pressure to remove it.
I have a couple of rubber plugs which are around one inch in diameter,
which were used in boats which I owned in the past. Those plugs should work
well for this application, if I understand how it is set up.
Yours Truly,
Clifford Wilson
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