I heard of something once that worked like form-a-thread I believe.
You put a paste on a worn area of a shaft and when it cured you could
machine it back to the original diameter.
We have a shaft in an old horizontal mill. One end is worn about .030
and fits into a bearing. They have been running this machine slotting
screws for years but I want it fixed. This seeems like the easiest way
if it works.