Admittedly, it's not at all a big deal to tighten the top and bottom bearings on a tradition all brass rotary valve. BUT, wouldn't it be nice(and make a lot more sense) if those bearings were a serviceable part that could be replaced or upgraded with off the shelf standard parts?
http://www.mcmaster.com/#standard-sleev ... gs/=j1qbxz
There are lots of choices in both materials and dimensions... including PTFE, and self lubricating bronze.
I would imagine a situation in which, rather than re-plating old rotors, swedging old bearings and lapping to fit, you would just replace with a new rotor and install new bearings in the casing.
Discuss among yourselves.