Supercharger issue

The tolerances in a supercharger are very close and unless the correct procedure is followed, you might have happen what your (very smart) mechanic is trying to avoid which is to have the engine ingest bits from the blower. Have you considered outsourceing the repair. When I worked on BIG trucks, the turbochargers were removed and sent out for periodic rebuilding as a preventive measure. Downtime for a big truck is better if the time is chosen rather than waiting for the unit to fail. These same folks might be able to guide you through the process. Google it and see what comes up.