The shutter on the 104 is rather simple. Other models have a more elaborate exposure system. Allowing you to choose a scene based on lighting conditions.
Whatever model you have, they all come apart the same.
Remove the 4 screws.
Notice the one by the shutter release cable is longer than the others.
The front should now come free completely, leaving the circuits behind.
Exposure control knob; electric eye
With access to both sides of the lens, clean the front element thoroughly. Don’t neglect the electric eye lens either.
The white dot is the exposure control.
Exposure control movements
When you turn the exposure control it moves a tinted piece of plastic up and down in front of the electric eye.
Move the piece all the way down so you can clean the back of the electric eye lens.
Circuits; electric eye red arrow
If the inside of your circuits are really dirty, you may have to really clean them, check electrical contacts and movements of all parts.
Luckily this one was really clean, so its only a quick once over of all the moving parts and keeping an eye out for anything odd looking.
The electric eye and shutter mechanism are on the right.
Fold down or move out of the way the boards so you can clean the lens element behind.