crank out bathroom windows

A home owner from Lincoln Nebraska says:
Have 2 bathroom crank out windows that will open with no problem but when closing they will stop with a couple inches left before completely closed and the crank will just turn as if stripped. Not sure what part may be needed to fix. I have enclosed a photo of what the arms look like but not sure that is what the problem is. I think the windows are Traco.
Thumbnail of the uploaded file named IMG_1232.JPG
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Manuela from SWISCO responded:

Your operator looks very close to our 39-239B operator. Take a look and see if you agree. Is this operator the original operator that was installed in the window? How old are these operators? Get back to us and let us know. I will forward this over to our senior expert, once you get back to us, to see if he has any additional input he'd like to provide. 

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