I'm pretty certain that it's not a lack-of-lubricant issue. The dead stop,
when it happens, is an abrupt halt, not an increasing-resistance petering
out of movement.

I'm not sure exactly how these blinds function but there's a curious runner,
unlike any of the others and not attached to a slat, which appears to be
playing a part in the problem. I just tried to upload a picture to my
website but discovered that my FTP program doesn't seem to be working any
more.