Today I have taken out the NEO motors and blow them with compressed air. There was some brush dust. The brushes are 12 mm, which is OK. Commutator - clean copper. :-)

I have Curtis handset. When operating the rocker from side to side it shows 100% right & 82% left. I have calibrate it a few times. Well, I think I did. I never receive an confirmation from the Curtis handset.

Once, while turning right, WAVE stopped and the handset was showing 100% right from potentiometer.

I've changed the complete left handle again and controller also from another WAVE. The customer will run it for a few days and will see...

Good idea about the castor wheels. I will check that also.