Hello. This has happened to me twice.
The cheap nylon rollers that slide along the channel guides break up after time. They are riveted on, so they want you to replace the entire regulator mechanism. I managed to find a close replacement for the roller a few years back for my rear window, and it has worked fine so far. Only cost me about $4 to fix what is a systemic design problem. Eventually everyones roller will break up and the window will jam.
In my case, I found a 25mm diameter nylon wheel with metal bearing but it was too thick. I filed it down to 5mm thickness. I then went to the window mechanism and filed off the lip of the rivet on the operator arm. I drilled and tapped a thread up the centre of the rivet. I fitted the new roller over the rivet shaft and then screwed a metal screw into the tapped hole to stop the roller coming off. Use thread lock if needed.
I have just had my passenger front mechanism fail the same way.
I am about to start the search again for a suitable roller. If I find one, I will be buying enough for all windows i.e., at least 6. If the thickness is too great, this time, I will have to pay a machinist to machine them all down, as it takes ages to file down and swarf ends up inside the bearing which will reduce its life span.
I would obviously prefer to replace with the original nylon product (even if it has a limited lifespan) if anyone can tell me where to buy them ?