Fenestra/Detroit Casement window crank

Would you mind taking a few photos of your original window crank and uploading them so we can take a look?

I would begin by taking a look at the 39-001 and 39-002 Window Crank Operators.

They shouldn't be too difficult to replace. You usually have four screws in the base that attach the operator to the window frame. After you remove the housing base, the long arm with the bearing should just slide out of the window track below the window sash.