I assume you mean the diff on the gearbox and not the rear diff on the rear axle, because if you mean the EYJ is the rear axle diff it just isn't.
Ive decided to break the car anyway, it was bought as a breaker anyway, thought I might keep it but there would be more money/time needed to be spent on it and its the best thing for me to do, might buy another C5 S6 early next year