With the back off the camera, run a test roll of backing paper through. As you advance the film see if it is actually slipping or maybe hanging on one of the rollers? If not then it can be the signal arm needs adjusting, a counter problem, not a damage problem.
To get inside, you'll need to take the top of the insert off. 2 Screws are inside from under the plate and the other 2 are on top at each corner. The lever has a large screw in the center under the leatherete. Take the large screw off, remove the lever and replace the screw before opening up the back so the spring doesn't slip. No big deal if it does, you'll figure out fast enough how it goes back... just a PIA wasting time. When taking the top cover off, watch the little metal slip on hte top right side. It slips out of the slot and is put back the same when putting it all back together again.
My guess is the ratchet n pawl is slipping on the advance. Common problem is from being forced, it cracks the pawls or the springs let go. A cracked pawl is not easy to replace n not worth the time. The springs can be put back in place or makeshift replaced. The signal arm is an adjustment.
BTW FIW, damage to backs most times is due to quick winding as if in a hurry, and allowing the lever to snap back. These are the most common causes of damge I've been seeing in backs these days.
