Since I had a"for parts" body to learn on...the film advance release button affects nothing as you remove top. Just 2 screws under rewind knob, two under film advance knob. Unscrew eyepiece. Clean only the glass lenses. Do NOT touch the diagonal glass with rangefinder film on it or you will be using a zone focus camera...no longer a "rangefinder" going forward. Adjust rangefinder if you are adventurous, but hopefully not.