In article . com,
Ancient_Hacker wrote:

The case
is sturdy but the plastic knobs and nylon gears are crumbly.

AH-

I talked to one person at a Hamfest who claimed to have done what you
are doing. He said that he had some custom metal gears made to replace
the crumbly nylon gears in the units he refurbished. If you have a
sizable investment, you might consider doing that as well. It should
completely eliminate that as a failure mode.

I haven't opened-up mine, but have one with a broken meter needle. I
suppose it is floating around inside the meter case, and it might be
possible to glue it back if I could figure out how to get to it!

Fred