Modern Vespa

My odometer stopped just as it was rolling to 20,000 miles. Speedometer works well; I check it against the radar boards on the roads at the gov't. facility where I work.

I need the odometer to work so I know when to change the drive belt and not have it break when I'm several miles from home because it gets pretty tiresome pushing my scooter that far especially when there are hills involved.

Is this going to be a professional repair or do I to spend all day removing body work to get to the instrument panel so I can shake and beat on the odometer to get it working again?

Speedo working but not mileage, maybe check if cable has come loose somewhere or replace cable and cross fingers that the little plastic gears inside are not broken.