So, I went out of town this past weekend, about ~250 miles each way in the MKZ. About 50 miles into the drive home, I started hearing a scraping sound from the right rear every time I hit the brakes. I stopped to take a look, but nothing stood out.
By the time I got home, though, I had a nice groove about the width of my thumb in the rotor on that side. Unfortunately, work got in the way, and I've had it parked a few days while I MOSTLY drove the MG(although I had to drive the MKZ a bit).
I finally made it to Autozone yesterday and picked up a pair of rotors and a set of pads. I'm really particular about fronts since they're so important, but just went bottom of the barrel on the rears.
In any case, after struggling in the past with retracting rear pistons(most FoMoCo products with rear disks use the disks for parking brakes rather than drum in disk, and as is common for that design, the pistons have to be turned while being pressed in rather than just being pressed in like fronts), I took out a $60 loaner tool. This is a slick device with a set of dies to fit a variety of pistons, and will both turn and push the piston at the same time. It took me longer to pick the correct die than to actually retract the piston, which is a big improvement over trying to push and turn at the same time with a set of channel locks.
When I got the passenger side brakes apart, I unfortunately found that the outer pad was down to the backing plate, and the inner pad was badly grooved. I'm not sure what's going on with it-I'm going to have to keep an eye on it for signs of a sticking caliper, although I haven't noticed the car pulling or anything else that would indicate an abnormal problem with that brake.
I should also mention that these are 46,000 mile factory pads and rotors. I'm use to getting ~80,000 miles on rear brakes, and it's even more bizarre in light of the fact that the factory front pads are getting thin but are still serviceable. The driver's side rears still had a LOT of meat, but of course I went ahead and changed them too since I'm not going to just do the brakes on one side.
In any case, even cheap rotors are pretty when they're new
I'll also add that I hate the pointless use of torx screws to hold the rotors in place. I started in on the fronts a few months ago(high spot on the rotors that's more annoying than a safety issue) but got stuck when I didn't have a large enough Torx driver to get them off. I'd since bought one, but haven't actually attacked the fronts again yet. In any case, I understand that the screws are mostly there to hold the rotors in place on the assembly line before the wheels are fitted. There's really no consequence to leaving them out, but of course since my replacement rotors were drilled for them I went ahead and put them back(with a dab of anti-seize).