Mamiya Press 100mm lens retraction issues

A year or so ago, I bought a Mamiya Super 23 with the silver 100mm lens. It should be retractable--had the markings--but wouldn't budge. Otherwise it works fine. I later bought a second 100mm lens--the newer black version, and it retracted fine. I used it for about a week, staying in the extended "normal" position, and then when I tried to retract it, it was totally jammed exactly the same as the silver one. I didn't do anything to the lens that I'd expect to affect this mechanism. I put them both away, frustrated that I couldn't try either with the body's bellows for close-up and tilt shooting.

Fast forward to today, I pulled them both out, and suddenly, the original silver lens retracts totally fine, exactly as the black one did right after I bought it. But the black one is still stuck. I did absolutely nothing to make this lens start working. When working, both rotated and retracted with very little effort. When jammed, I have applied a scary amount of force trying to get them to budge. Like trying to open a stuck jar force. (No pounding on the edge of the counter though.)

I am so confused! I can't find any mention online of this problem. But it seems like an impossible coincidence that I'd have one lens that spontaneously develops the problem and another that spontaneously has it go away if it isn't a common issue.

Is there something I'm missing? Has anyone else experienced this?

Try pushing the inner sleeve from behind with your two thumbs. You'll need a little lubrication in there as well, they get dry and friction builds up making it difficult for the pins to line up.