UPDATE: Campfire Time suggested fabricating a replacement for the worn part. The problem involved a particular part, sort of a cam latch, that just would no longer engage into its slot, and so the bike rack would no longer lock in the upright position.
Pursuing Campfire's idea, I put the bike rack up onto a big work table under a bright light to see exactly which portion of the latch was causing the problem and how a replacement could be fabricated. I was all set to take some measurements for the welding shop.
As I was examining the latch mechanism, I noticed a thin sliver of steel -- almost too small to see -- that had wedged itself into the pivot point of the cam latch. Hmmmm. Maybe that sliver was part of the problem??
There was no way to reach the sliver with tools to cut it or file it -- not even a needle-nose pliers could get at it. But there was a thin hole or slot above the sliver. So I took an old sanding belt and cut off a long strip, about a quarter inch wide, and fed it through the slot. Holding both ends of the strip of sanding belt, I worked it back and forth, the same way you'd polish shoes with a strip of cloth (back in the days when we wore shiny leather shoes -- remember?).
After about fifteen minutes of "sanding," the sliver was worn away. The latch mechanism was freed up. Problem solved (at least for now). There will come a time, fairly soon, that I have to replace the whole bike rack, but not yet.
