Lesabre window track

I have a 88 Buick Lesabre. This morning I rolled the window down, heard it snap and it would not come back up. I took the door panel off and found that the slider in the window track was broken. I got another one from a dealer, however I am having problems getting the new one back on the track that is attached to the motor. The old one was difficult to get off as well. Any ideas????