casement winder 'skips teeth" and no longer pulls window all the way cloased

It definitely sounds like you need a new operator. We can help, but in order to make a recommendation I will need you to disconnect the long, straight arm from the track and show me the guide at the end of it. We carry a few different styles and that will help me narrow it down. Yours is currently too obscured by the track to make out.

Thank you! This operator is a match for our 39-253RB. We also sell the 39-253LB for the opposite side, as well as the 39-452 and 39-451 covers/handles, which are sold separately. Finally, we sell the slider itself, which is our 39-529, but yours appears to be in good condition and you can likely reuse it.