I would not suggest trying a rebuild of the unit.

I scored the long side of the top with a razor blade until I could get the fine blade of a screwdriver in and chipped away at the side until the cover would pull away from the base. altho' it's not a "sealed" unit, mine had NO contamination. And cleaning would be the only thing you could do besides increasing the tension on the brushes. If the unit is worn, my advice would be throw it away and buy new.

Now about that Hub Tamer...

Collins
I'm amassing WAY to many old Suby parts...