These are the storm windows that have an aluminum frame screwed directly on the outside of the window frame, and the screen and glass panels slide up and down, depending on the season. Over the years the panels have become damaged (bent screen, cracked glass). Can I buy and insert the replacement panels myself, and what are sources for that? Since my house is over 80 years old, will I have trouble finding sizes (the current storms are about 20 years old). Is replacing the inserts cheaper than having a contractor replace the entire thing -- aluminum frame and insert panels? Thank you.