+1
There is, or has been, someone on ebay selling their own version, but I found the cost difference is minimal, and ordering them from Hasselblad was very fast and easy.
In my experience nine times out of ten the actual light trap is fine but the foam has collapsed or gone gooey. I buy sheets of 1mm thick foam from Micro-Tools, remove the old foam from the foil using goo-off and replace it with new foam. Each sheet is 8$ and would make about 50 seals. Only takes about 10 minutes per back.