Hurd 18 inch by 54 inch (glass size) casement window operator
Thanks for posting. Sorry but this isn't enough information to be able to help you. Can you show us a picture of the operator, preferably out of the window, with the link arm(s) in full view? A bird's eye perspective is often best. From there, we'll try and see if we have a match. Many thanks.
Thanks! This is a huge help. Take a look at our 39-387, this looks like it could be a good match for your old operator.
That said, based on your description of the issue, you should examine the condition of your hinge, as well to make sure it isn't damaged. That may be the source of your issue.
One easy way to check is to disconnect the operator from the window and try closing it by hand. If it still hangs up, then the hinge is what you want to replace. If it closest without issue, then the operator is the culprit after all.