I've never looked at an rdb monty. Are the calipers the type that slide on the caliper bolts? Check the bolts for any crud and corrosion,, then I'd replace the piston oring (probably a square edge ring), AFTER I polished the piston with 400grit paper. Unless the LSPV is seriously pooched, it should not trap backflow to the MC reservoir when you come off the brake.

You might try spinning the wheel with the suspension loaded (jack stands under the axle) and with the suspension extended (stands under the frame) both before and after brake first apply.

Next, do you have the right brake hardware, especially the shim between the piston and pad. To properly retract, the pad has to "stub" its leading edge on the disc, and is usually cocked to do this slightly by the shim which has a partial cutout in the piston/pad contact area. If it doesn't stub, it's likely to drag some and heat up the brakes.

Also check the ebrake cable for proper adjustment and release (this one has shoes in the disc hub, right?).