Hasselblad 500c light leak

Buongiorno,
I am italian and I write a terrible english... I hope to be clear enough, though.

I have a problem with my beloved and old Hassy 500c.

I am experimenting light leaks on my negatives, they are vertical and they run through all my frame, in the middle of it. They do not seem to affect the non exposed areas of the film.
These leaks are not in every negative, but they happens, sometimes 1 or 2, some other times they just are not there.

Usually, before shooting, I push the button on the right part of the body that releases the mirror etc. I do it because I am afraid that all these mechanical movements could affect the sharpness of the negative.

Here is my thesis:
Sometimes I forgot to keep the shutter release button pushed until the shutter finishes its work. I mean if I've choosen to shoot at 1 sec, first I push the mirror button, then the cable release. But if I let go the button before the end of the second I could have light leaks, but they are vertical and not horizontal as they should be, since the mechanism works horizontalwise... (and this is the weak side of my thesis)

Thank you very much,
regards,
Carlo

Carlo,

I think most blad owners have had a similar experience with the mirror lock up button and letting the cable release go prior to the shutter completing it's exposure.... I know I have!

What you are describing would typically give you under exposure as the film has not had the full second of exposure before the closing trap doors cuts it short. It does not explain why you are getting light leaks vertically on the middle of the frames. Unless one of the trap doors is loose and not closing fully or is out of sync with the mirror and light is being reflected some how through the gap in the trap doors??

Have you tried taking the back off the camera and cycling through all of the steps you would take to see if there is something hanging up some where? By that I mean slowly winding on to reset the shutter to see what happens to the mirror and doors while you do this, trip the mirror lock, and then trip the shutter, and wind on again. Look for anything that looks loose. Can you post a scan of these negs for us to see also?

Thank you for your prompt answer.
The inside of the body looks perfect.
No things hanging.
I cannot post scans and I try to describe it:
the light leak fades from its axis (where is lighter) gradually to the sides. So it is a leak that has some shadings from the center to the sides. And all this line is from 7 to 9 mm large.

Oh (I forgot!). I will do the test you suggeted me as soon I will be back home where the Hassy is!
I think you are right about something somewhere reflecting light.