yes this can be done. chop away cement bed cill under cill, u/screw cill if you can see screw head at bottom of door frame. If not run a hack saw blade between cill & frame to cut screws. lever cill down to break silcone seal , New cill ,new silcone, wedge up to door frame and screw through frame into new cill. (not a easy job but can be done) .
david 30yrs a d/glazer, December 2005