Rear diff vibration from 45,000 miles. It still drove OK, but got very gradually louder until a reconditioned unit fitted at 60,000.
Water Pump leaked and drained coolant from engine 50,000 miles.
Seat motor made noise, but failed to move seat.
Exhaust twisted due to engine/transmission movement needing welding 50,000 miles.
LCD in clock faded.
Boot button sometimes failed (but remote and dash buttons worked!).
Counterweight in ashtray cover broke - ashtray bangs open rapidly when opened!
The car was indeed quick in straight lines, but heavy and terrible at corners. The 'traction control' cuts the power for 2-3 seconds leaving you dead in the road if you pull out of a junction with slight gravel present - I am not sure if this is the same for all x300 1994-1996 XJRs.
As others have said the interior even on the older x300 1995 straight 6 was a pleasure to get into. The car made me smile when I walked up to and sank into the seat!
The problems I had all came with the car, it just took me a while to discover them! I was always able to drive the car, but I did opt to pull over for a while when the temp gage rose above 50% and straight into the red for the first time in over a year of everyday use. The water pump had a leak which required a fill up of water and coolant until it was replaced at £240 plus labour.
Unless you buy with the optional uprated Harmon Kardon sound system then the basic stereo is OK, but no better than Mondeos or Cavaliers of the same year.
A good independent performance garage is essential for out of warranty XJR's - the type of garage where they can take a differential apart or weld your exhaust manifold. Jag dealers seem bound to repair cars by swapping units. I was quickly quoted £1500 for a diff and nearly the same to fit it. A new exhaust was recommended at over £1000 for the parts alone. The independent garage welded the exhaust no problem and fitted a £900 reconditioned warranted differential for £600 labour.
I fell in love with the shape, power, prestige and comfort of the car as did many passengers, and this makes 90% of other cars in the same price bracket feel plasticky and cheap.
Petrol (14-18mpg round town) insurance and servicing considered, an XJR will cause a serious rise in your monthly spend.
Do your research on the Nikasil and timing belt tensioner problems affecting the V8 cars from 1997 up to 2000 and even early 2001 if you are looking to buy.