Hi Mark, and welcome to the club.
The XJ is the top off the range Jaguar, and was used by Royalty as well as Senior members of the government and still is.
I was offered one 8 years ago that had been used by the Queen but I have an an L shaped drive and my s type carefully misses the bay window, which the xj could not do.
Yes I would take the car to a good Jaguar mechanic and have all the fluids including the il in both engine and gearbox - a good car needs a good meal as it were.
My s type has done 87,000 miles and is a very smooth drive and it does get the treatment every year and it is only 14 years old.
It sound a real good buy.
Regards,
Peter.