Zenit E Mirror problem. Mirror doesn't lock up in Bulb Mode

Hello.
I bought Zenit E in really good shape. Everything is smooth and shutter works correctly. But few days ago, Bulb mode stopped working. Shutter works correctly, it stays open when I lock the shutter release button. But mirror doesn’t lock up.

I’ve opened the Mirror mechanism cover and noticed one thing: when the shutter is pressed, mirror goes up, curtains are opened but the mirror falls down like on 1/Xs shutter (the lifting gear doesn’t stop in the locking position). When I release the shutter button, Curtain is closed, but the Mirror mechanism doesn’t move at all, like it should. Can this be fixed or not?
Here is a slow motion video on Youtube:



Thanks a lot!

-Sven

Maybe the best Zenit repair resource is right here in this forum: https://www.photrio.com/forum/threads/zenit-em-complete-cla-ongoing-thread-pic-heavy.178883/