Plastic bits within the sunroof/moonroof track and slide assemblies are notorious for getting brittle, cracking and then failing. Not just an Expy thing. The repair is a lot of labor (from what I've seen anyway)
Probably not something you want to do on a newer Expy, but if you can get it closed manually, then you could pull the fuse and just leave it closed.
We had a 2003 Chevy Trailblazer hand-me-down. Disconnected the glass and removed it, manually manipulated the slides back to the closed position and re-attached the glass. Then left the fuse pulled. If you go this route clean out the drain holes while you are in there and verify water flows through. Leak expert told me to use string trimmer line. Then park on a slope then poor in a bit of water. It should disappear down the drain hole and drip out the bottom of the vehicle.
For that 2003 Trailblazer an aftermarket kit of replacement tracks and slides was not expensive. I saw them as cheap as $30.00. But after watching a video on the effort required... it just wasn't worth it to me. -- Drop the headliner, remove the entire moonroof track assembly, drill out some rivets, install the new bits, then put the whole thing back together, etc. If this was the only issue with that trailblazer, I might have done it. But it had bigger problems....