Stuck lens on Mamiya RB67 ProSD

The 90mm lens on my pro-SD seems to be stuck & impossible to remove.

I press the shutter lever forward all the way, the mirror comes down

as far as it will go, & the mirror comes down, no problems.

Then I try to rotate the lens ring in an effort to get the dot on

the lens ring to match the dot on the top front of the camera face.

The ring won't budge either direction.

The camera works fine, I took several rolls with it today. The mirror

goes up and down happily. I am missing something else with all the

interconnected mechanisms? Should the film slide be in or out, or

doesn't make a difference (doesn't seem to) I have even tried

removing the back.

Yes, I have posted this on the Mamiya site but am hoping someone here

can help me too.

(note to Mamiya's technical writers: your manual can use some

improvement, Example:"counter clockwise" doesn't mean much unless you

specify whether the camera is pointing towards or away from you. And

your troubleshooting section merely points me back to the

instructions, which I already knew about!)

With the lens pointing to you, turn the ring in counterclockwise direction. You need to move the red point on the moving ring to the red arrow on the lens (or to the red ball on the camera body).

Some of the lenses I have require significant effort to dismount but you should be able to turn the ring by hand. If it does not go, take the camera to repair-shop and they should be able to loosen it for you.

Mamiya's manuals seem to be translated by somebody who does not know English well (on the other hand, they are easy to find for free).