Hi all, kinda new to these forums was well as to analog photography.. I've got a RB67 Pro SD and a Mamiya Sekor C 3.8 90mm lens; my problem is that I can't manage to screw/mount the lens on to the body.. It aligns correctly but when I go to turn the "mounting ring" so to screw on the lens it only turns slightly and pretty much jams on to the camera and is even harder to take off.. I realise that if it is not fully attached it is unable to cock the lens fully. (The lens in the photo below is not cocked, I did cock the lens to the green dot before attempting to attach) Your help is much appreciated guys! Below is a photo of how much I can screw it on.. should go to from 12 o'clock to 3 but this is as far as I can move it.