Driver side door (retracting black bar on door) replacement

Hi, my vehicle is in great shape but some parts are getting worn. There is a black bar on the door that attaches to the body and retracts into the door panel. It is making noise, looks worn and it is getting harder to open and shut the door.

I do not know what this part is called. I would like to try and purchase the part online to save money. But since I do not know what it is called I cannot.

Thanks for your help.