I had the same problem and I emailed All-Clad's customer service department and they just asked for my mailing address and sent me a replacement whistle (free of charge) in less than a week. Good luck!

It's hard to answer any kind of questions about insulation without knowing what part of the country you are in but the proper insulation and air circulation is always good.If it's paper faced I would guess it is fiberglass,The grey color could be from moisture ,dust or dirt of everything being not sealed properly intrusion or many other factors. Bottom line is,without more info,when opening up walls to do this extensive work it's always good to make sure you have the proper insulation.Can't tell you what that would be without more info and a location.

I've done some more research since my OP - my reason for changing out the old wood-clad for vinyl (instead of wood-clad) was to save money. The wood-clad sliding patio doors that I like are Marvins, and they are very expensive. The hybrids do not seem to be much of money savings over the wood-clad. If you are saying that vinyl, which will save me money, won't look nice, then I may as well go back to wood-clad, and try to find the budget for a good wood-clad sliding glass door. What is the next rung down in price from Marvin wood-clad sliding patio doors, but still good quality? I know I do not want Pella. I am hoping the kind people on this forum will suggest a good bang-for-the-buck brand in a wood-clad sliding patio door. Thank you.

More suggesting it because there are options to have a wood interior with a non-wood exterior. Wood is great and a lovely material, but there are better options in many cases if you are not compelled to use wood via some sort of historical guideline.