Found a stripped-out FD fill plug :( Repair recommendations?

[Yarddog]

When I bought my R100 the same fitting was already replaced with what I think is called a well nut. It is a rubber plug with a machine screw set in it that screws into a nut fixed in the other end of the rubber plug. When you tighten the screw the plug gets thicker and seals the hole and it cannot fall out. Sure, it is a bodge repair that I found when I first replaced the FD oil but that was nearly 30,000 miles and three FD changes ago. I mean to repair it right when I have to remove the FD for some other problem but for now it works fine and will never strip out.

Kinda the same general idea as those rubber expanding freeze plugs referred to earlier...however, I believe that the well nut might be able to fall back in, whereas the freeze plug won't...but the smallest size available is 3/4"...it's a Dorman part...