When replacing the screen and finisher make sure that you put plenty of sealant at the lower corners of the frame so that the water does not sit in the
corner and rust the frame. If it has already rusted here then clean and scrap it thoroughly and treat the area with your favourite rust preventative. You have a choice of sealant/adhesive to mount the screen. The original used
an electrically heated strip to cure the compound but you will find that the professionals now have a range of more easily applied adhesives.
As the finisher is just held in place with the adhesive you might find it useful to use a few wooden blocks, duct tape and string at strategic places
to hold in the finisher in place until the adhesive sets.