993 rust bubbles below front screen

[brian7136]

Just looked at 993 with view to purchase. Lovely car but has the dreaded rust bubbles on the front scuttle adjacent the screen rubber for a length of about 75mm in line with the steering column. How big a job is it to let in new metal? The screen has to come out presumably, but does the dash have to come out? Any experience of cost out there? Does it suggest corrosion problems elsewhere?