Need help identifying Cadillac door part.

I have a 1993 Cadillac Sedan Deville and I have a small rolling wheel that rolls everytime I open and close the door which is between the door hinges that's tearing up and I need to replace it.

I very likely will have to go to the dealer to buy the new part.

Does anyone know what this part is so I can tell the parts man at the counter what I'll need? Thanks in advance for your help.