Retapping would be best, but since there's no pressure in there, that leaves room for some creativity. You may be able to find one of those rubber plugs that are used to repair freeze plugs on engine blocks. or perhaps one of those rubber plugs the boyz at Jiffy Lube use when they punch a hole in your slushbox pan to change the ATF....

As long as you check whatever you use periodically and it is secure enough to NOT catastrophically fail ( but just leak a bit)....

How about something as simple as a toggle bolt with a rubber disc backed up by a plate keeping it tight?

Rick

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