Bar soap is one thing that will work.

What are windows made of? Wood, metal or vinyl?

Are the ballast working? On older windows ballast would be attached to either chain or rope. They may may also be pressure controlled.

On newer windows u will see a nylon cord.

U can spray track with D40.

Chuck

White silicone grease works great on aluminum and vinyl windows.

Hi, sjnowak!

In addition to the other fine answers, how do they appear to be difficult in opening and closing, please? Just by sliding? Or, could something else be making it difficult? Something coming apart, etc..

Thanks!