Gears on the crank are stripped and the mechanism needs to be replaced.

Gears on the crank are stripped and the mechanism needs to be replaced. I cannot get the crank mechanism out without pulling off the lower frame of the window sill. The piece could have been installed in the 1950s when the house was built. Before I tear apart the window frame I want to make sure that this piece might replace the old  one. I have an engineer friend who will help me install. We'd like to keep the existing pieces except for the crank and metal bar that comes out of it.