Nikons DP-3/12 ring resistor and
Sovers super DP-3/12 ring resistor

The Nikons DP-3/12 ring resistor is very delicate. The metal contact fingers are only 5 microns thick, and they wear out (cut through) by the wiper brushes after 250,000 rotations. This sounds like a lot, but under professional use (100 rotations per day, 200 days per year) the life of the Nikon ring resistor is only 13 years. Hence many DP-3s and DP-12s have bad ring resistors inside, and their meter LEDs are very unstable as a result. Since there are no more Nikon ring resistors available, these bad DP-3s and DP-12s were often trashed.

However, I now have replacement DP-3/12 ring resistors available. My custom made ring resistor has a super hard carbon ring with a life greater than 1 million cycles. (Please do not confuse it with the dreaded Nikon soft carbon ring resistor inside DP-1s & DP-2s.) So its life is greater than 50 years under professional use. I can therefore give a life time warranty on my super ring resistors. That is, the DP-3 and DP-12 meter LEDs will never become unstable.
Nikons DP-3/12 ring resistor Sovers super carbon ring resistor
Rig used to test the ring resistors.
The carrier spun at 2 rotations per second
for several days.
Nikons ring resistor contact fingers were cut through
after 250,000 cycles
Sovers super carbon ring resistor had only
very minor wear after 1 million cycles.
The ring resistor with the test carrier was then tested inside a DP-12, and there was no meter LED jumpiness. Even I was amazed.