Direct Drive Turntable plays slightly too fast

I have a nice realistic turntable that is a direct drive. I just took it out of storage in its original box, i might add, but I just noticed after reading the instructions that the stobe shows it plays slightly too fast.

I adjust the speed knob all the way it will go in the slow position, but ever so slightly the strobe shows the platter moving a hairs length clockwise - or too fast.

What can I do. Is the speed knob a potentiometer? Should I replace it? Can I add a 100 ohm or smaller resister to the potentiometer? Is it possible to pot oxidized?

ideads please?