Yes, replace the motor. Very common failure. Suggest you do it now because the cold will slow it down to the point where it won't move.
To get at it you have to pull the door trim panel off, which is a matter of disengaging the clips along the front and rear edges and the bottom. Find the clip by prying (gently) up on the plastic trim, and pry to as close to the clip as you can to release it. Once the clips are released, you have to slide the door upward to release two more clips that are behind the grab handle. If you have a hard time getting those to disengage, reach up from the bottom with a stick, place it near the clips and tap the bottom of stick with a hammer to move the clips up to release.
When the panel comes off you will see the two clips slide into two white plastic retainers that are still in the sheet metal. When you reinstall the panel, remove the metal clips from the door trim (tricky, use needle nose pliers) and slide them on to the white plastic retainers on the sheet metal. Position the door so the holes in the grab handle area line up to the clips, and a couple of smacks with your hand in the grab handle area will reseat them.
Once the trim panel is off, you will notice a large plastic sheet (water shield) that has to be removed to get at the window motor. This is stuck to the door with the nastiest, stickiest black stuff man ever invented. Otherwise known as butyl. You have to peel the plastic, and then remove all the butyl from the plastic and the sheet metal. If you don't do this properly you will get water leaks. Note how the bead of butyl dips at 3 places along the bottom of the door at each of 3 drain holes. It is important you follow that same pattern with the new butyl, making sure you do not block those holes.
You can buy the butyl at any automotive paint and body supply store. Ask for the stuff used to install windshields on older cars. I think the rolls are 15' and come in two diameters. Get the smallest diameter (3/8"???). Should only cost $10 to $15 for the roll. Do not try to save money by buying some sort of 2 way tape. This will lead to water leaks.
With these 2 tricks of the trade (how to release the grab handle clips, and butyl tape) this whole exercise is a relatively easy repair. If you get stuck, come back to the Bonneville Forum and post your issue so we can help you through with it.
Most important, when it is all done and your window is working again, come back and tell us how wonderful we are, and how you couldn't have done it without us.
2001 Bonneville SSEi (retired at 365,000 Kms.)
2014 Jeep Grand Cherokee Overland (yes, I know its not a GM)