Bollocks mate, what a ballcahe as you were saying it was 'supposed' to be a really low mileage box too
seeing as you've got the diff (one of the expensive bits) why don't you give cts a call and see how much to rebuild yours, as when mine went last year they only charged me 350 to rebuild as the quaiffe was fine......shot peened gears were an extra 350 on top of that which i WANTED but was told as they didn't have any there would be a minimum 6 week wait, and tbh they'd already had the bloody thing for a month!!!
Think it might be worth a call mate, as a 2nd hand one will cost you more than 650 i'd have thought....