And this is why I do my own maintenance....
So the reality is that the rear right caliper somehow lost a bolt and so the trailing edge was allowed to push the pad at an angle. I also learned today that F350 brakes do not have the usual squeal bar to indicate pads needing replaced....
So the inner pad was gone and almost all of the backing plate was worn through making it into a wedge. The movement was enough that the piston was able to push free of the bore, thus causing the leak. That scary part (besides missing the break on I85 N) was that the inner face of the rotor was worn about 2mm! The truck gave me no indicatuo s that it was having an issue so I just didn't know.
So here comes the kicker.... I had just paid Quick Lane service to do an oil change and service. This was 2000 miles ago. The tech had written that all the pads had 4mm material left.... In swapping the brakes I am finding that all of the pads each were at a different thickness. That A-hole literally measure one and then just marked them all as that ans missed the fact that there was no pad left, the rotor was half as thick, and the caliper was missing a bolt!
I had a talk with them today on my parts run and was able to come to an agreement that Quick Lane was paying for the caliper as that would still have been salvageable had the tech so much as looked to see the brakes were shot.
Glad I didn't get hurt and neither did anyone else.
