As luck would have it, I have the whole thing apart right now as I'm replacing the radiator. Looking at the assembly, if it was me, I'd pull the whole thing and put a bolt through the hole with some sort of sealant like silicone.

If it's not a round hole, you can probably use some fiberglass mat and JB weld working from the inside for strength.

__________________
-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250