Question on Mamiya Sekor 55/4.5 for Mamiya C TLR

I just received this lens after won a bid on ebay today but the C330F which I received early is on CLA. After inspect the cosmetic condition, I start to test the lens and found 2 issue.

1. When the M-X syncro selector is at "X", everything looks fine. But when I turn to "M" I cock the shutter and push the release lever, the cock hit back but not fully and the diaphram don't open and close as it should. I have to push "a little" so the diaphram will work, open and close according to speed I set. Is this normal?

2. Does this lens aperture ring has click stop? On 80/2.8 blue dot it has, but this 55 I just got hasn't.

Thanks for the answer in advance.

I think I have all the Mamiya lenses except the 105 with the depth of field preview, and my memory is that some of the aperture rings have click stops and some don't. Regarding the M-X issue, you will probably never have a reason to use the M option. That option is for old flash bulbs. Today, almost all flashes are electronic strobes. I have seen some folks tape the little lever to X so that it doesn't accidently get set.

And the 55 is one of my more often used lenses. Enjoy!

There are two versions of the Seiko shutter. One has click stops, the other doesn't.