I'd be wary of plugging it with a plug that fits like a grub screw. Stuffing one of those brass fittings in an aluminum housing rarely ends well. If there's any corrosion you will end up stripping the wrench hole out of that soft brass.
I'd use a plug with a regular bolt style hex head.

We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon