there was recently a thread on the practical machinist forum about those types of pumps. dammit, i might be thinking of arduino vs evil. or both, i can't recall.
not something you can just throw together, or repair. more like trade secret voodoo involving edm, polishing/lapping , running the pump for a certain number of hours, perhaps with very, very fine grit in the oil before you ship it.
anyhow, i do apologize for incorrectly expecting a lot more than the 5% current reduction you achieved by boosting the voltage 10%, but, were your measurements true rms ?
anyhow, as i mentioned earlier, shorted turns are almost always catastrophic failures. you can't just dump a half kilowatt of heat into a single shorted turn, to account for the half hp of missing shaft torque, and not expect the motor to warm up.