Rear diff oil leak

[Saff]

Hi, my D4 passed its mot yesterday which is great news. It also had an advisory on an oil leak from the rear diff. It appears to be from one of the driveshafts ( diff to wheel). Obviously this needs to be done asap. I’ve had a quote from a specialist, SR Miller in Standish, Wigan of £671. This entails removing the exhaust and the diff from the car and replacing both seals whilst it’s off. Millers seem to have a good reputation and much of the car’s servicing is from there.
Does this sound a fair price for the amount of work involved?
Opinions welcome, cheers Steve.