So my theory gets tossed in the Thames
as both the motors are 4 pole, so should turn at identical rpm.
The only suggestion that I can offer now is to connect the replacement motor directly at the wall socket. I have read reply #6 but that did not mention where the "direct to mains" point is, inside the gram cabinet or on the wall.
This is the only suggestion that I have at the moment as it would confirm if there is any issue with the replacement motor or the supply point in the gram.
Edit : What is the voltage rating stamped on the bottom bearing of the replacement motor? Dual voltage or single voltage?
Regards,
Anwesh