Weaver Shark Pickup Rollers

While replacing the control electronics in my 1990s Weaver (Samhongsa) Sharknose, I found the pickup roller on one truck to be immobilized and the one on the other to lack conductivity into its supporting arm, even after cleaning and exercising them extensively (this loco has had minimal use since I acquired it 25+ years ago).

Does anyone know if replacement arms are available somewhere?  Or has anyone else encountered and resolved this problem?

The roller has pins on either end that seat in the arm ends.  Significant resistance exists between the roller and each pin.  The "usable" roller has an effective resistance of around 2-3 Ohms to its pins.  The other one has essentially infinite resistance.  These aren't just DMM resistance readings. I ran a 12 volt power supply into a 10 Ohm resistor via each arm and roller, measuring a voltage drop across one assembly of 2.5V @ 0.9A and a voltage drop of 12V across the other. 

I have other locos with similar arms, but their roller diameters are larger and not suitable for the Shark, as they raise the truck and thereby minimize tractive effort.