Good work Brett,

When I get your other bad one I will see if it also has the same and if if so why ?

At least you know how to correct the problem rather then having to spend another $100 for the 4th master.

I suspect release bearing had jammed, up and down on pedal but since bearing could not return back the fluid in the slave could not push the fluid back into the master and caused some issue to be found later as plunger is a unuseable state.

Yes without a doubt the condition of brake fluid does not cause this problem where pedal never returns and when it problem occurs but then corrects itself.

I'll do images and writeup once I get your's and fully analyze it.

At this point we now have a cure for the problem you had and how to correct it without buying another master.