I recently bought a Mamiya C220, and it's in excellent condition and working very well. I'm happy with it.
This is not a problem, per se, more a curiosity, but I believe the focusing screen in the camera may not be the stock Mamiya C220 screen (the seller didn't mention this).
My understanding is that the standard screen has two parallax correction lines, one very near the top of the frame that corresponds to the 1.5X exposure factor on the lens distance scale and a second one roughly 1/4 into the frame (from the top) that corresponds to the 2X exposure factor.
My screen has only the second line — i.e. the 2X exposure factor line. I'm attaching a picture. One thing that doesn't show in the picture is that the entire screen, except for the central clear circle, has very thin black concentric circles line etched in it.
Anybody have an explanation for this? Is it a third-party screen, or an optional accessory screen from Mamiya? Again, I'm not concerned, per se, just curious; it works fine and focus is perfect.