That's actually a new one for me! I have the "newer" design if I'm not mistaken, but I'm assuming construction is similar. I've never seen one mechanically be bad, it's usually the gears break. I think what you're experiencing is the sunroof doesn't know exactly what position it's in. Unfortunately these sunroofs are actually quite crude. It uses a bit of mechanical circuitry in the gear mechanism to tell the controller what position it's in. When the gears wear or skip some teeth, it'll stop before it reaches open or won't shut all the way. Unfortunately they made these gears from plastic. A new motor won't fix it unless it's the motor's teeth that are stripped. Basically, you need to drop the headliner to access everything. In gm's infinite wisdom though, you can't get to the gear box except from the upper side of the sunroof assembly. What I've done to avoid removing it completely is to remove all but the rear screws and loosen those and use something to prop the assembly on. It'll drop enough to reach the screws to remove the box. If you're lucky and the motor gears are stripped, you don't have to do this, just replace. Tricky part is the position. The roof won't move manually without the motor removed. So before all of this, open the sunroof as far as it'll go, then remove motor, manually open it the rest of the way, and re- install the motor. Lubricate and clean the tracks with silicone lubricant and test. Should be all good!
