It turns out that many households have the problems and there are lot of helpful videos.
First is what Scott has done in two parts:
This is the part I.
This is the part II, that shows a very good outcome.
My Honda mower stops engage the self-propel capability, this link provides a detail instruction on replacing the driving belt.
Here is the repair steps video.
This guy provides his suggestion.
A detail operation video is here.
Get the clamp fixed
Part on EBay
Part on PartWarehouse
Diagram on Makita parts
This seems to be the correct part
The manual of Makita JR3000V, from the official Makita USA