I recently bought a RC4WD Reduction unit and altho I like it it was a little loud and the bushing was not happy with the load I was putting on it. So I replaced the Brass bushing with a Bearing that I found at Mc Master Carr
shaft is 6mm = ID x 10mm OD x 3mm thick with a flange.
simply put a dab of loc tite on the flange and push it home. I ran it for 2 hrs tonight pulling 5 bricks on my 48' flatbed. has a little less noise.
Just thought I would share the upgrade. I will report back in a week to see how it holds up
RC4WD 4:1 unit
This pic shows the bearing ready to be installed