Crunchy weirdness with power windows

Hi all, first-time poster so first off, hello and thanks for reading about my problem. I hope someone can help.

For a while the passenger-side power window has been a bit funky. It would roll up about 3/4 of the way, then stop and wind back down another 20cm or so. We found that a bit of encouragement from a hand would get it to go all the way up and stay up. Later, we discovered that it'd also work fine if we opened the door before rolling it up.

Yesterday these 'fixes' stopped working. The window won't roll all the ray up at all; if we try in increments it goes *almost* all the way then stops and rolls down again. There's also a nasty crunchy noise.

I took the door apart to have a look. It's definitely not the switch. The motor (when removed from the door) works smoothly and quietly, so it's not that. I found no apparent obstructions anywhere. I tried lubing up wherever I could reach, too, to no effect. I *did* find a fairly heavy bolt flopping around in the bottom of the inside of the door...

I guess the actual mechanism of the window is horlicksed somehow. I can't for the life of me figure out how to get in there though - it seems to be sealed inside the door. Any ideas what I can do? I'm seriously brassic at the moment, so trying to avoid taking the problem to a garage until I'm sure it's not a reasonably easy fix.

Thanks for any and all advice!