Second floor casement - new to us home

Thanks for posting. Unfortunately, when that gear piece (called the worm gear) pops out with the entire handle, it means the operator mechanism has broken down and must be replaced entirely. We likely can help, but I need to see the entire assembly, including the arm(s) that push and pull the window sash. A bird's eye view, with the window open so everything can be seen, would be best. We'll do our best to find what you need from there. 

Thanks for getting back to me. It's admittedly still a bit tough to tell from these photos, but my first guess is you need the 39-348 Awning Operator. Compare with the diagram below to confirm; if anything seems off, explain why and please send a picture from a bird's eye perspective; I'll be happy to find something better. For a new handle, see the 39-114L sold separately. If your old shoes and track is damaged, see the 36-078 and 36-078B. Let me know if you have further questions.

detail of 39-348

Great! I agree, I think this is a winner. Please feel free to reach out if you had any other questions, though and we will be happy to assist.