Looking to replace crank mechanism

Thanks for reaching out! It sounds like your casement operator gears may be stripped, so its a good thing you are looking to replace the entire mechanism. 

Your casement operator looks like it could be either our 39-253RB or our 39-439B; the opposite handed version of each of these operators are the 39-253LB and 39-438B, respectively. 

To confirm which of these is the correct replacement, you'll need review the video below. Take note of the differences between each operator and compare them to your existing hardware to confirm which of these you need.