How can I fix my Carl Zeiss Werra camera?

This classic camera went out of production about 30 years ago.
It had a well known problem, the shutter jammed if you pressed the exposure button while at the same time winding on the film. This was easy to do and meant a trip to a camera shop to have it fixed by a camera repair man. Old time camera repair men familiar with this kind of camera are now hard to find. It should be an easy job to release the shutter mechanism if you could find out how to get inside. This is not a focal plane shutter but is integral with the lens. Some models had removable lenses, the one I own has a fixed lens, and I cannot figure out how to take it off to get at the shutter mechanism. Removing four small screws inside the camera which look as if they should secure the lens doesn't help, they just loosen the lens wichi is still prevented from coming free by something inside.