There's no contact or wear in a b-less motor other than the bearings.
Preventative maintenance would be to keep the thing cool and clean, though if properly insulated they can run just fine completely sumberged with VERY little decrease in performance.....
Basically just don't let it overheat. It can destroy the rotor (easily replacable) but more importantly overheating can damage the insulation on the stator wires taking your speedo and motor in one go in a burst of sparks and smoke.
Jon