My mate has been told that his RRS rear differential is goosed and he needs a new one, he has been quoted £750, questions i have are , should this be a fault on a 5 year old car with only 70k on the clock, is it worth contacting LR for a contribution and what is likely to have caused it to fail.

Any help appreciated

if you don't ask you wont know.

Depends if the Sport has full service history and whether LR might think it been used for heavy towing.

I suspect it will be a slim chance; remember if you ask nicely you might get a contribution. "you catch more wasps with honey than vinegar"!!