I agree that the washer should have been replaced at the time of the oil change....why it wasn't is a mystery.....probably best answered by bean counters....
Now if it had been a copper washer to start with then perhaps annealing would have been appropriate....though whether there is anyone who knows how to do this, or even has the time to do this at my dealer's is anyone's guess.
I suspect that from a business point of view it is a lesson learned - a total of 240 miles (there and back twice) on a trailer to drop the oil, install a washer that could've been replaced during the oil change and then refill the gearbox and monitor for further leaks - and maybe in future the washer will be replaced as a matter of routine (in spite of what the bean counters say!).
