NH 6740 disc mower problem

My grandson was mowing last week with a New Holland H6740 disc mower and noticed the cutters had stopped.  When I inspected it I found the pinion gear in the module under the gearbox had stripped.  Module to replace it is over $500!  The dealer has the gear kit available for $235. 

 

Has anybody replaced this gear and will share the instructions on how to do it? 

 

Thanks

NH 6740 disc mower problem