"Cost was $135, which makes me wonder if it's a good idea to buy older machines with nylon gears! Granted, it sews exceptionally well, but still - what if it happens again? Seems to me there were at least 2 more of these in there."
Look at it this way: The machine gave how many years of good service before this happened? (and I would probably have had all the gears replaced) With the new gear you can reasonably expect that many more years out of it. That some good machines have nylon/plastic gears or camstacks is just a fact we have to live with. It's up to us to decide whether we think the machine is worth repairing(the ones that can be repaired). And with the advent of 3-D printing, it won't be long before many that are delegated to boat anchor status now will be able to be repaired in the future.
Cari