op1 gents best advice if its persistent would be to get one off downer car they are around £200 - 300 if you look get one from same year. trade parts .com etc
the oil should be then changed - 30,000 mile and you should be ok. go to independent jag garage labour 3hr approx to change. oil cost £30-40
that's it should be sorted. fix it ,keep it, if you like it
op 2 put your diff in to engineering workshop with new baring seal kit and have it refurbished. may be difficult to find one near you ask local mechanic they should point you to someone that can do gearboxes etc
all in should cost approx. £500 fitted or do it yourself for 230 ish
I'm a diy mechanic not pro and sorted mine as op1
hope this helps and apparently its not common issue so just unlucky or the oil has been neglected to be changed.
check youtube for videos if you plan to change the oil etc
