Riso GR3750 print drum cylinder not installing

[el_mustango]

I recently got a Risograph GR 3750. When I got it home and fired it up, it was giving me a T1 Call Service error. The person I got this machine told me I would need to resolve some error codes, so this wasn’t unexpected. I tried to remove the print drum and couldn’t using the standard methods, so I manually unlocked the print drum using a long screwdriver pushed into the hole just under the drum. There was a master stuck to the print drum which I removed. However, now when I try to reinstall the print drum into the machine, it goes almost all the way in but stops and I am unable to get it fully inserted and in the locked position with the green handle all the way down.

I’m a fairly handy person but I worked on this for several hours and wasn’t able to figure it out. I’m sure this exact question has probably been asked and answered on this forum in the past, but I can’t for the life of me find it. Any help would be greatly appreciated. Thanks!

[20gaugeO/U]

Is the drum locked in home position? Silver clamp plate area at 12 o'clock. If so there is a key pin coming out of the back wall and chuck drive on the back of the drum. To much slop in either one can make it not line up. Hope you didn't pay anything for this machine. My suggestion, scrap it and find something at the very least in the RZ line, even better EZ. MANY many many parts for the GR aren't available and haven't been for a long time