After using the STX guider for about two years successfully, It appeared the guider shutter wasn't opening. I removed it from the optical train and saw there wasn't anything preventing the shutter from moving as I could move it easily back and forth with my finger. I did find a small nut in the bottom of the case. see attached pictures. The pics show the shutter in the open and closed position. I couldn't tell right off where the nut would go. 1) should I be able to move the shutter with my finger easily? 2)does the nut shown in the pics indicate that's why the shutter isn't operating? 3)where does that nut go exactly? Awaiting any help, thanks