Mamiya 645 S1000 AE prism viewfinder aperture pin

I have a Mamiya M645 S1000 with an AE prism viewfinder. This viewfinder has a pin that should click into the aperture lever of the lens.

Normally there is pressure on this that pushes the pin down and fixes it well in the handle.

Unfortunately this does not work properly any more. Sometimes the pin is pushed down properly, but usually it stays pressed against the top of the viewfinder when a new lens is inserted and the aperture ring is turned to lock with the pin. It appears the spring is not working as it should anymore...

Anyone have any idea how to open the viewfinder? And then further?

I've been pondering how to open these, as well. In addition to needing to clean the contacts on a metering prism, all of mine suffer from damage to the prism coating (apparently related to the mounting material).

There does not appear any way they can be opened from the bottom, so that leaves screws under the leatherette. I haven't had a chance to try that surgery yet, but it's on the list.

Just today I had a closer look at the finder and the mechanism. I noticed that when I pushed the pin in, to a certain point it would still spring back correctly.

Here I noticed that the pivot arm was very slightly bent... and when pushed further in, pressed against a plate inside the finder. It was at this point that it stopped working and I felt increasing resistance.

A careful push in the opposite direction to remove the bent, and that did it!

Now a happy owner of a beautiful M645!

Has the silvering of the prism not been damaged? Nearly everyone I've seen has this problem.