Replacement sash balance mechanism

It seems like the string attachment to the window channel is supposed to be a small hook which is missing from the metal piece at the end of the string. I have included a picture of the window channel hole that I believe the string should attach to. I have also shown photos of a broken and not broken plastic retainer piece in the window edge itself. The balance is 25 inches long.

These are 35 year old windows from a manufacturer that is no longer in business called Weathervane Windows. I believe they were primarily a Northwest manufacturer of windows. Our house is located in Woodinville, WA.

Thanks,

Paul