I bought a 127 mm for my RB67, and although everything cycles, the shutter is slow on all speeds.
Fifteen or twenty years ago, I might have tried to give this a cleaning myself, but these days a) I know my own limitations better, b) I don't have a good work space, and c) I don't have time to get the work done without it sitting for a long time, inviting parts to disappear.
So, who does good affordable work on the shutters in RB67 lenses? It'd be a pretty straightforward round shutter if not for the way its cocked and triggered...