I am going to disagree on the walk of the dark color and rubber release agent of the rubber parts decomposing. Because if the rubber did decompose, then the quad ring would also decompose and if that decomposition is going on, then that is a fast rubber eating down to a leak out the caliper tolerance is that rubber loosing seal.
I am going to say it is more oil color change is that burn; caused by the heat from the caliper area. I will also state that maybe the oil boils and you cannot have a vacuum in that boil and now what was in between the res cap and the air you just squished in between or say the water boils and what is in that bubble but vapor. So say the oil is boiled, water is the contaminant. Water is now heaver than oil, settles under the; 'decomposing rubber"; creates a crystal effect (name for wires turning white by the battery sorta look at the same action but in the acid state); then pushes the rubber up against the caliper quad ring (like your quad bike) and hangs up the disc or your brake pads are hanging up if not pulling the piston back from the memory of the Q-ring, but now is dragging on the discs upon release.
So, if I take that theory to the clutch master, could I not use a scenario that the piston in the clutch servo is that piston chatter as it walks forward or back because of all the goop under the rubber quad ring? I doubt very much me thinking about changing a toilet rubber flapper and that rubber is sure decomposing right in my hand does it leave trace like GM Wrench intake manifold sealer in a black tube is the, Rezzz Sea Dew in my fing gears.
