Hi, thank you for your reply!
When I raise the mirror by finger it goes all the way with no sticking. What exactly is the mirror lifting bumper? If it is the small piece of foam that keeps the mirror from hitting the top of the mirror box when it is raised, then I believe it is fine at the moment.
When I first got the camera when the shutter was fired the mirror would do a small little jump (as if it were wanting to lift up), but it would only be a few millimeters. Since that side of the mirror box couldn’t complete the full cycle, I would use the mirror lock knob to reset it, which would complete the firing of the shutter. If I leave the mirror locked up, the camera is able to fire on all shutter speeds just fine.
I am beginning to believe that the mirror lifting spring does not have enough tension, since there is no other obvious mechanical failure. If there are any other photos of videos I could show you to help you see the issue, please let me know! Thank you so much!