yup, that happened to me, too. I reinforced the inner fender and frame. then the z-bar arm peeled off of the zbar tube. reinforced that, and so on, and so on.
This happened almost 50 years ago. If I were doing it now, I'd think about a multi disk clutch, so you'd have less pedal pressure, and less load on the stock linkage.
If you don't want to make that leap, it might help to optimize all the geometry on your linkage, to make sure there are no extraneous side loads, slop in the bushings, joints, excessive wear, etc. not only in the zbar area, but in the throw out arm and even pedal assembly.
