It is a monumental job to replace a filon exterior wall. The filon is glued to a substrate, the substrate to the frame. The process leaves an adhesive bond that is very strong.
If you only have delamination in a few areas, a repair is possible but may not be a permanent cure. The repair process involves insertion of an epoxy underneath the exterior filon and bracing until the adhesive cures. Some have had good luck with this repair process.
If you have delamination, I would suggest to check for leaks using the "pressurized interior" test. Seal Tech is one commercial company that does the test or you can do it yourself with a blower. The pressure test turns up even pinhole leaks.
Good luck with the repair!
