Used to hose out mirror boxes with lighter fluid, now I use a $12 squeeze bulb and a brush
For years I cleaned mirror boxes the way an old timer in Baltimore showed me, which was flood the whole thing with lighter fluid and blow it out with a rocket blower. It worked, sort of, but half the time I left streaks and once I melted a bit of foam near the prism on a customer's AE-1. Two winters back I got a Nikon FM in with a foam seal that had turned to sticky black goo, and the lighter fluid just smeared it deeper into the finder. I sat there with a magnifier for maybe 40 minutes picking goo out with a toothpick, and that was the night I gave up on the flood method. Now I do it dry first, soft brush and a squeeze bulb, then a barely damp pec pad on a plastic stick only if there's real gunk. The whole job takes 10 minutes instead of 30 and I've had zero comebacks on dust since. Curious what the rest of you use for that evil foam residue, because I still hate it.