I pulled my old FE out of the closet for the first time in years. The mirror was locked in the up position. I checked that battery, not the problem. I removed the bottom plate and released the lever that locks the film advance, cocked the advance lever and the mirror released (speed dial in M90 position). But now I have a new problem - every other advance or so the shutter releases as soon as the advance lever is cocked. The other time the advance is normal and the shutter release button works. Any thoughts on how to fix this?