Tristan,

I had a RR caliper start leaking too. I replaced the seals and it continued to leak, wound up replacing the caliper.

I use OEM type pads in the rear and have not had a problem. It seems to me like you have a caliper hanging up due to the fact that only the outer pad came apart. I would check that the pins are straight and the holes are not worn. If the slider holes are rounded out some, it may cause the piston to cock and screw up the seal.