Oh my word. I can’t believe I’ve found this thread. I have twin 250 G1. We have the port hand gearbox fail at around every 200hrs. You could almost predict when it’s about to go according to the hours. BRP are useless in the UK and will not even talk to the customer. A hopeless product! Dover Sea Safari
Your dealer need to be sure that the replacement gearcase are counter rotating units. They will have a C and an R on the end of the prop shaft. With the electronic shifting system a standard gearcase will get programed to run in reverse and have a very short life.