Two more points on this broken window-lifter issue:
(1) Million Mile Sprinter will have his regulator part
back in stock this coming week.
He actually has them fabricated by a supplier, hence the delay. I'm guessing that his is a better design as well, because it appears to roll as well as slide.
(2) Even if you do NOT wish to preemptively replace your hardware, you would be doing yourself a big favor by opening up your door (remove the trim) and using a good solvent to clean out the track, then place fresh grease in there.
We found that the grease had deteriorated so badly that it literally was acting like glue. I think the plastic part snapped due to friction in the glue-that-was-formerly-grease.
In other words, it was a tensile break. The plastic part got stuck in the "glue" and then the actuation arm snapped it in half due to the resulting resistance.
So who knows - if you simply solvent-out the grease and replace it, your plastic bits may never break.
This video shows the door dismantling process, and it also shows the "no hardware" replacement option. Dude thinks he's found a good way to fix it permanently, but I notice that he didn't do anything to remedy his glue-grease. So, I'm wondering how long the motor and gears will last under these operating conditions. He is correct in that the arm mechanism will never break again. But his gears might strip.