From the pictures I would say the leak is on the film-canister side of camera. Or it could be on the take-up side if you use a film canister on the take-up side.
In this picture:
as you can see: half is overexposed and half is as shot. The border between those 2 looks just like the film leader at the beginning of film - one part is exposed, then there is the border (as from the felt stripe) and then unexposed...
Or it can be leak between the back door and the top cover. There should be a "yak string" but you better replace it with some modern material (as Noel said cut it from mouse-pad). Like in this picture (linked from
Kiev survival site):