I am trying to repair a small, button-fill, Gold Starry pen. I have removed the fragments of the old sac. However, I have run it to an issue with the barrel and/or nib-section threading. It was incredibly difficult to separate these intially but trying to screw them back together is even harder. It just gets stuck at the beginning or partway through and won't budge any further. I have tried to clean it but I don't know if there is much to clean. It kind feels like the threading isn't aligned correctly? But I'm not sure. Any suggestions or insight would be much appreciated. Thank you!