This is my guess also. There is probably a washer that takes up end play that maybe got left out. IDK the design offhand but that shutter is fairly simple.
Originally Posted by Jon Shiu
Try this, take the back off again and see if there is excessive endplay (side to side) in either of the rollers.
With my motorcycle they even have different gauge washers so the endplay is exact and you measure it with a feeler gauge to a certain spec. I'm sure the graflex shutter doesn't need to be this exact but I thought I'd just throw this thought out there.