I have just officially saved myself about $120 at the very least. Why? Because I decided not to send my new-to-me Mamiya C330 to a camera repair shop to have the light seals replaced. Instead, I bought a repair kit on-line from ebay for about $10 including shipping, and did it myself. I did try this earlier using the self-adhesive soft half of a strip of Velcro without any success at all, so I'm really glad I found the right stuff to use this time.
The images below are from two different rolls of long expired HP5 (2002) that I used to check the results. Woohoo! success! There's no discernible photon penetration in places that shouldn't be penetrated by photons especially in the upper 'graph which was made in very bright and intense sunlight. And, happily, the film itself seemed to have done well despite its alleged terminal status.