I have an extensive Mamiya Universal System with multiple bodies and several backs. The light trap is not dependent on the foam seal. It's a mechanical trap and as long as contours are still closely matched I've never had a light leak with any of my backs. The foam is always dead on these. Gooey nasty stuff. I have a "near" direct replacement for the cable release. Identical but about 1 inch shorter. They were used for many years on Polaroid C4 tektronics CRT cameras. I can send you one for $15. Works on all of the Universal lenses but perhaps the 150 and 250mm. I always use a tripod and a seperate cable release anyways as a remotely held release button cures shake. Try giving your 100mm a harder twist. It should have a "high" spot it bumps over to lock in place. The other lenses for this system are all excellent. The Mamiya is my "color" camera. I'm a LF B/W guy but when people require high quality color I don't waste my time with expensive 4X5 chromes. I have many 20X30's in public places made with the old Mamiya and Velvia 50. The 50mm wide angle is Superb! Worth more than you paid for your whole system so far. It's a Zeiss Biogon copy. Do yourself a favor and don't buy one without the finder included. The accy. focus screen is worth it's weight in gold for anything that the finder won't tell you like macro etc.