Dear X5er's

my wife's 2003 3.0D was serviced recently and one of the problems diagnosed was a leaking input shaft seal into the rear diff. It is a 400+ km round trip to the nearest dealer so I took it to my local mechanic who works on my other cars and he is not sure he can do it for want of special tools to 'preload'(?) the diff. Is he being overly cautious or is this a difficult procedure.

Thanks for any advice!