Potentiometer Rating

My stir plate is quite old it appears as though the potentiometer is shot. I tried cleaning the ring on the back of it, but it has no impact on it. It is basically working like a switch between off and on at full bore.

So I need to replace the potentiometer; however, it does not say on it anywhere what the ratings are, thus i don’t know what to replace it with. I tried googling ways to find out how to find out what i need, but i have found nothing. Can one of my savvier brewers help me on this one?

What, if any, markings are there on the pot?

That’s exactly my problem there are no ratings or serial numbers on it at all.