My two cents (sense?): I have a feeling that there is a tiny bit of oil in the shutter blades, preventing clean, quick movement. What I would do (and please do not do this and blame me for helping you wreck the beast).
I would remove the bottom and open the back. Then I would squirt a bit of lighter fluid onto the shutter blades, always holding the camera upright so that NO fluid gets into the prism area but, instead flows out the bottom. I would do this while operating the shutter. Then I would place the camera, again right side up so that prism does not get any fluid, into my oven. My pilot light keeps the camera about 110F. Overnight the body should be dry but, occasionally, I would fire the shutter.
This is a tricky endeavor and, again, I offer warning. But I have done this to success. - David Lyga