If a M/C has a seal capable of 'rolling over' & making my brake system ineffective, I don't want it on my ride. The fact that he thinks thats possible would be enough for me to return it. Measure the bore, get a bolt spacing dimension, take that info to a good parts hose & speaking of NAPA here, they'll have a paper catalog with this info. Pick a commonly available one that meets your needs. You will be able to replace/rebuild it for years later in any town. Beware of poorly engineered/quality controlled aftermarket components, usually made offshore.
Just my humble opinion here.
Good Luck, Doug
