Doctor Diff Master Cylinder

I've wondered about things like that. If he is selling these under his brand, they are most likely new and sourced from Asia. I dealt with Chinese-sourced parts in the last 15 years of my career and dealt with QC issues CONSTANTLY.

My opinion is they should last a pretty long time. I'm just spit balling here but the cylinder bores should be anodized at a minimum for wear resistance.
My old Direct Connection aluminum MC is still hanging in there. Knock on wood.