I've had good luck with 35mm cameras using a cotton ball lightly dampened with rubbing alcohol and rubbing it all over the leather/metal surfaces. Alcohol will dissolve some adhesives so care must be used but the cotton balls come away the color of coffee so I clean a good 80-90% and the remainder has faded in 30-60 days just sitting out. I've done a half dozen e**y wonders and they are quite usable.
YMMV so do so at you own risk.
Fred
YMMV so do so at you own risk.
Fred