One of the garage doors stopped working, only went up a foot. I found the gizmo that rides along the center rail disengaged.

To get the door open I had to pull the red cord and push by hand.

I managed to work the controller so the two parts hooked together and got the door to close. Fixed! ????

But then when the door was tried again, it went up about 18 inches, groaned, and again the two couplers uncoupled.

Back to the research. looked today at this video:

This suggested that some lithium grease spray on the rollers is needed ongoing and luckily I had a can.

And darned if we are not back in opening business! Saves me a call to the Garage Door guy. And also reminds me to lube the rollers on the big door on the Quonset hut (I suspected the chain might need some)