dont know the full ins and outs, but went in for a service and inspection, they found a tooth half broken on the gears somewhere, i did see picture, cant remember what tho.
new parts and fixed including service and some other small bits .... £15k !
lets not forget though, you'd be talking about incompetent dealers too.
The probably just replaced the entire trans, as I really doubt anyone would ever let them disassemble and rebuild something like that. Dealers tend to change oil/filters if you're lucky, and wash cars.
In depth knowledge and repairs....not so much. There would be very very few skilled and competent mechanics within the dealer network.