No I did not.
What is interesting is the T for the rear brake line. The driver's side is a rubber line connecting the Tee into the caliper. The passenger side (the failing side) is a hard line about 3 feet, then about an 18" section of rubber line. Is this the normal configuration? I supposed if the lines are different ID then the one with the smaller ID would get the most pressure. [edit] however the 18" rubber section for both sides sort of negated that theory.

I ordered some brake pads, although the pads were not worn out. My thinking is the wear on the pad is sufficient to cause the caliper piston to overextend.

If you have any thoughts, please post. One thought I heard is the driver's side may be sticking or plugged (it bled out fine though). I also thought maybe the gizmo which regulates the pressure between the fronts and rears has failed such that the rears are getting too much pressure... but why would only the passenger's fail.

Something must be wrong if I've gone through 4 calipers in 4 months on the same wheel.

 

I've had the rubber lines come apart or 'shred' on the inside causing the caliper to be held on which heated it up and caused it to fail. New caliper and it did the same thing, held on until it ruined it. I had this happen twice. When the front does it it is much more noticeable due to it pulling and shaking. The back, I didn't notice until the damage was done. By searching on the net and calling the brake shop that did my SUB, I found that replacing the rubber lines would probably eliminate the problem. I did and it worked. As far as the proportioning valve being bad, I kind of doubt it even though they have been known to go bad. Maybe someone else can chime in and give you some more help. When you get it figured out, please let us know because as you know most of have a bunch of miles on our Xes.

 

I finally got around to tearing apart the hub and sure enough it was a blown seal; I also found a destroyed inner bearing at the same time. I guess I should have done the seal sooner; oh well.