Hi That's a five.
Fitted a second hand fan from a Honda 125 today and this motor will spin CW and ACW on Gas Gas with engine running, depending on which way round connectors are fitted. Having stripped both Honda and Gas Gas fan motors from their respective mountings, they both have a directional arrow on the label on motor body that shows the motor should spin ACW. Motor functional - One problem solved!
Am liking your latest diagnosis re partial failure of rectifier, although new motor will spin quite happily both ways whereas the original motor would only spin CW. Now I will recheck voltage across the new motor for both DC and AC and look to fit a new rectifier if reqd.
Bill