Hi Jeff,
If The Worst has happened, all is still not lost. The outer portions of the boss might well be re-tappable as Andy says, or retapped and a Helicoil (thread insert) installed, making it serviceable again with essentially no change in appearance if the threads have been torn out.
LocTite make a stripped thread repairer called Form-A-Thread (
http://media.midwayusa.com/pdf/instructions/Loctite_stripped_threads.pdf ), but I have yet to try it.
One very late night, I received a call to a remote location where a friend had stripped the threads on an oil pan fitting. Lacking a Helocoil, I made the repair with some JB Weld, which was later tapped for threads. It held for the next two years with nary a leak, and was still going strong when he sold the car. The difficult thing was getting it de-greased properly, but you wouldn't have that problem.
As a last bit of encouragement (no matter how unlikely or dim), could it be the rack tang is offset just a bit and keeping the bolt from entering properly? If the boss threads did strip, perhaps it is just in the outer portion. Thorn's threaded bosses are pretty long, so it seems unlikely the entire length is routed out. If there are still some threads remaining, can you run an extra-long bolt through the boss and secure the other end with a nylock nut? <-- That will work even if there are *no* threads, and I've done the same on my own bosses, which are okay. In fact, it is not a bad idea (as I did on my Miyata 1000LT a couple decades back, and as Andy Blance suggested on my Nomad) to run the bolts from the inside out, then secure with a nylock nut. If the worst should happen and a bolt snaps, you can still remove it without need for a drill and screw extractor in some remote locale.
Remember, Thorn do offer replacement forks and a few even show up on eBay occasionally, so that option is possible as well.
Hope this helps.
Best,
Dan. (...who firmly believes where there's etching polyamide/polyamine epoxy resins, taps, and rethread kits...there's hope)
