The Hasselblad Historical site has a good how-to for replacing the light trap. http://www.hasselbladhistorical.eu/ht/htseal.aspx
I have done it several times, super easy - about $10 delivered for the seals. This is what the set consists of, your sinner pretty obvious here
Hm, my kit was different from yours, and didn't include the thinner seal on the upper right of your image. (Nor was it mentioned in the instructions.)
Clearly it was needed. I put the seal kit on today and the result was as follows:
First here's the old seal. the screwdriver is touching the remaining part, and the exposed foam is above, where that other piece got torn off.
After replacing the seal I ran a roll of film through the camera today and the old corner light leak is fixed, but now there is this:
The film appears properly sealed on the right edge where the worst problem was before. That's where the dark slide is inserted, right? I'm wondering if the missing third foam strip is causing the rest.