Thank you very much for your input, Simon! I did many studio shots and none of them have issues like this. But almost all my field shots do have some sort of light leakege. I also painted inner parts with a black permanent marker prior doing outside shots.

I find my negs quite contrasty but incredibly sharp and I've never noticed any problem regarding uneven processing - now that I can exclude this and regard my problem to light leakege.

I love the camera, even with the flows it has. Especially the fact it's so light!

Thanks again!