lower unit plug issue on 9.9 johnson

I noticed some lower unit oil on my outboard yesterday not long after using it that has to come from the upper plug. I figured the plug got loose and I would check to make sure water did not get into it and put the new lower unit oil (or gearcase grease) in. To my surprise (or horror) the upper plug will not tighten and spins freely. I figure there can be two things wrong. Either the plug is bad (which I doubt but I will check) or the threading in the hole where the plug goes on the outboard is bad (the motor is from the 70's).

If it is not the plug but instead the threading on the motor that is bad, are there any fixes? I checked Leeroys but did not find this issue.

I'm sure guys on here know how to go about a fix.
Here's another option: Ask.com--------How to fix a stripped lower unit plug on an outboard
That should bring up a bunch of info., from various sites, from others that had the same problem.

Wonder if you could use a Helicoil insert?



CMOS

I think it's thin for a helicoil. Plus you'd have the dissimilar metal thing to deal with.

I'd try to run the threads with a a tap and if that didn't work go up a size and replace the plug