If the rest of the braking system is working correctly, it stops ok, and doesn't pull, you could always just use a die grinder to widen the gap on the retainer a little. The retainer is only there to keep the pads from coming out. It isn't necessarily a precision part.
I still think that one of your pads has worn more than the other, leaving the rotor offset in the caliper, which would make it offset in the gap of the retainer.