Edward A. Falk wrote:

It's ocurred to me that a decent machinist could make a living just
making after-market replacement parts for this and other shoddily-built
avionics.

In all fairness, the NAV122 is a 20+ year old radio. I doubt Narco
expected them to still be in service this far down the line. Nylon is
lighter and far cheaper to make complex parts (gears) than machined
aluminum. I certainly don't begrudge their choice to use nylon gears
instead of aluminum.