I have an wooden upper window sash that slides down so much that it is almost behind the lower sash. The window is about 35 years old, but is in otherwise good condition. I've been told that this slippage is due to a broken spring. Is there any way to replace the spring without removing the entire window from the frame and taking it to a shop for repair? Thanks for any guidance!

If you don't need to open the top, have someone make a couple of 1X2 supports that will hold up the window. Otherwise, you will have to remove the trim and pull the entire window out, not worth the effort. Some older hardware stores may still sell stainless steel friction slides that work pretty well.

As a general statement, yes, provided you can find the needed part. Finding the part is the difficult part. Several different types of mechanisms. As old as the windows are they may have counter weights, not springs.