UPDATES
I called VPI, but was told they do not directly sell parts to customers. I had to go to a local dealer. The dealer was also not sure what the model of the motor was, and how to get the pulley off. He took pictures then sent to VPI.
Several days later, dealor came back with two options provided by VPI: $300 to change the 600 RPM motor to 300 RPM one, or $50 to only change the pulley.
$50 seems to be too much for a plastic pulley, so I chose the more expensive motor option
Now the motor works super quiet.
PS: the dealer strongly recommended me to keep the motor housing. According to him, my 20-yr old super heavy housing is much better than the ones on the motors of many recent VPI turntables.