Assuming a droput eyelet rather than a mid-fork...
either way, here's what I'd do:
- Remove the rack, and clean the threads (and the bolt) with a
brush/solvent. You may find that just the bolt threads were affected. You
may also find that it was only the first thread in the eyelet or so which
pulled out or was damaged.
- If it is clear that the threads on the eyelet have been _slightly_ damaged
(like one or two threads on the outside, from a too-short bolt), you might
try force-chasing with a new fresh bolt from the inside of the eyelet. If
you are all uneasy about doing this, skip to the next step...
- Take the fork to a good shop where they can chase the threads with a
proper tool. Might just be able to save it with no further changes.
- If it's toast, then the same shop should be able to retap it for the next
size up (5 to a 6?) with a minimum of fuss. Probably worth having them do
both sides so at least your rack uses the same bolt on both port and
starboard.
- If the eyelet lacks the meat to retap (and that's really doubtful, unless
it failed somehow), then you would have to get a new one installed, or go to
a p-clamp mount.
Hope that helps! Sounds like a great trip!
- Jim