Everyone says replace the light seals first, but on 3 old SLRs the real culprit was the mirror bumper foam turning to goo | Camera Repairers

Ray Hill · 2026-09-15T13:55:05.092627+00:00

Every forum thread about a dim or hazy viewfinder on an old camera says the same thing: swap the light seals and you're golden. I bought a beat up Pentax K1000 at a flea market in Fresno for $25 and did exactly that, full seal kit, carefully scraped out the old gunk, and the viewfinder still looked like I was peering through a dirty fishbowl. After 3 tries I finally pulled the prism housing apart and found the real problem. The mirror bumper foam up top had melted into a sticky black tar and off gassed onto the underside of the prism, and that film was doing all the damage, not the seals. I cleaned it with a little naphtha on a swab, replaced the foam strip, and the finder went crystal clear in about 10 minutes. I've now done this on a Nikon FM and an Olympus OM-1 with the exact same result, and nobody ever mentions it in the standard advice. So before you order a $15 seal kit, pull the lens, lock the mirror up, and shine a light at that top bumper foam, because that goo is usually the whole ballgame. Anyone else run into the melted bumper thing instead of the usual seal rot?

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Everyone says replace the light seals first, but on 3 old SLRs the real culprit was the mirror bumper foam turning to goo | Camera Repairers - The Design Community Hub