itself is no longer available.
On mine, the motor had overheated the bush holder, which I was able to repair with a bit of careful heat and bending back into shape.
The potentiometer is installed so the resistance is 5k-ohm with the ram at mid-point. If you need to replace the pot, make sure to get a 10k-ohm and one with the same dimensions, including the shaft dimensions.
I don't understand the "pinching problem" so have no input there.
If you need to work
on the motor, be careful removing the "can" surrounding it. It is a snug force fit into the cast housing and is easily distorted, so work
carefully. It is sealed with a small amount of silicone on reassembly.