I just recently got into medium format so I picked up an RB67 from eBay. I shot a roll of film through it thinking everything was okay. Later that night I wanted to go take some long exposures and realized the Time mode doesn’t work. I will shoot and the shutter immediately closes. I took the camera home and found out that when I fire the shutter, the mirror doesn’t go up all the way. I have to gently push it with my finger and then it goes up and then the shutter will fire. When I take the lens off the body it works perfect fine. Arm the mirror, fire, everything works great. But as soon as the lens is on the mirror only goes up halfway, or sometimes almost to the top but not enough to make the shutter fire. Any idea what this could be? The lens in question is a Sektor 90mm 3.8