The reverse fork in my tranny was fubared (it was stuck to the magnet on the bottom..) so with out trying, when down shifting from 5 to 4, it would just slide down to R, grinding, not a pleasant sound..
They replaced all the gears for mt, feel slike it's brand new again..
The thing is, I just has worn in the other gears, had 11,000 Km on it..
Good luck in the engine, don't give in, or tell them you want the warranty on the power train to start again, from scratch..