I think an easy project is to replace the steel wool excuses for motor brushes used by some Rivarossi locos with standard Athearn motor brushes which have been made to fit by rolling them on some sandpaper to reduce their diameter to fit. Sometimes that helps them run more smoothly. I have the NWSL wheels in the mail to eliminate the traction tires, which is a must if you want to avoid these things wobbling down the track (which is not totally unprototypical, I suppose). MS
I’d rather just put a good quality can motor in it and put some new trucks on it. I’m sure replacing the steel wool would help, but it would probably be better to just scrap the motor. Atlas RSD or FM trucks work for the U-25C, you just have to reuse the riverosssi U-25C side frames. There’s alot of room for a good sized motor to be placed in it.