Window repair

I would like to repair windows in my 33 year old home. The windows are double hung and are spring loaded on both sides. I can find no manufacturers name anywhere. A plastic clip attached to the spring and ultimately to the side of the windows are breaking and no longer help to raise and lower the windows. Needless to say, this is very dangerous and could easily injure someone. Attached is a picture of the plastic clip. Can you Identify the part from my picture? Thanks for your help. George