Mystery brake issue.

I appreciate the information, but I don't think I'm going to do that.

I ran compressed air through it, and there's no blockage, so any other problem that may exist probably requires replacement. If that's the case, then I will likely replace the entire master cylinder.

For now, the car stops fine and doesn't behave strangely in any other way, so I think I'm going to leave things as they are (unless I see some other anomaly emerge).