Borrowed from Ultimate Subaru Message Board 3.8.00 posted by Eric Zap-Chairiotsu
If the hole the post is in gets stripped, it
isn't a big deal to fix it. At your local auto parts store, you should be able
to find what's called a 'Helicoil thread repair kit'. The kit should contain; 1
drill bit, 1 Tap (re-threads), several helicoils, and a helicoil installer.
I recently performed this operation on my 86 HB.
I found it to fairly easy but will say this. Drilling into your heads can
play games on you mentally. Don't give yourself an ulcer worrying about it
and have some faith in your tools and handywork. My HB is QUITE a bit
quieter than it ever was before.
The kit was around $60 from Napa. I found this was the only place in town that had the correct bolt and thread kit.
Basically take your time, dont make it a 30 minute job the first time, and tell us about your success when you are through.