This is a casement window operator that I need to replace.

Thanks for posting! I recognize this operator. These haven't been made in a long time, and we don't know of a guaranteed replacement option. That said, I've known a few customers in the past who used our 39-390 as a replacement, but many others reported that when installed, the sash wouldn't close due to the show hitting the end of the track before closing. One fix for this would be to mount the operator base on the sill in a manner that would prevent this from happening. This is just an educated guess, though. Either way I think you can expect to have to play around with it a bit if you want to get it to work. Let me know what you think!