Beside the shutface pilar, this area is often rusted badly. However my car was not rusted these places also need extra attention. Not very strange these places rust away because all water and dirt are kept together inside lower part of the dash side strengthener. Maybe we have to drill one or more big holes in the bottom to prevent that water and dirt will stay there.
First I removed all material below the 70% (original material left) and then remade all missing parts. Sprayed again everything in zinc paint and welded everything back to there original positions.