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You're supposed to only apply it on the electrical contacts. Realize to be effective at removing chemical residue and finger goo it has to contain solvents. Whatever you do, don't spray any optical components like the reflex mirror, pentaprism or focusing screen. I normally spray a q-tip and wipe the contacts directly.
I've successfully used contact cleaner to fix keyboards but you need to disassemble it and clean the individual key switches. Just spraying the outside just makes for poor penetration, creates a mess and wastes expensive cleaner. I was surprised at how many hairs, cookie crumbs and dried coffee got down there...