Hello! This is an older type of operator, but we should still be able to help. The issue could be either the handle stem being worn down or the collar in the operator hole being stripped out. If you're in a pinch, you could use tape on the handle stem to build it out. That should give the operator a little more life before you need to replace it.
If you just want to replace the whole operator anyway, we will need to see a picture of the entire mechanism, including the arm that opens the window. Once we see that I'm confident we can get you a modern replacement.
Thank you for your reply!
I was trying to avoid changing the whole mechanism as there are a few windows with the same problem in the house. I was wondering whether it is still possible to find this type of handle anywhere. I would try this simple replacement first.
Thanks again!
O