Top window of double hung. One of the plastic "arms" seems to have broken off

Thanks for reaching out! The damaged shoe on this assembly appear to be an older, discontinued Simonton coil shoe. We suggest replacing it with the 15-259 Coil Balance Pivot Shoe. Take a look at the video tutorial below for a detailed explanation on the conversion.

To determine the correct coil you'll need to search for a stamp/marking on the metal. If yours does not have a stamp, take a look at the video tutorial, tagged below, for instructions on selecting the correct coil spring.