Could also be bad flex line. Rumor has it that as the rubber deteriorates the i.d. of the line becomes swollen which doesn't allow the fluid to return, basically keeping pressure on the caliper piston.
And when you say "left rear", you're talking about the driver's side, correct? Anyway as you're already aware, it looks like you get to do the brakes again. Just be sure to double check your installation and lube the crap out of those caliper pins. I have no idea why the passenger side pad was having that contact issue, my only guess is that something wasn't lined up correctly.
2001 GT Convertible
8 cylinders, 5 gears, red.
6 cylinders, 3 gears, also red.
Remember my motto kids: Be bitter, stay angry and blame everyone. It's on my fridge magnet!