hi allan jaguar say the gearbox oil should last the lifetime of the car. as do bmw audi merc ect. but in reality thats not true. some of us up here in central scotland 30 odd of us all jags old and new attended a tour at mackies automatic transmissions here in glasgow. a factory tour. and the sealed for life gearbox oil was blown out the water. mackies say that you should get the gear box oil and thers a filter in ther to changed between every 50-60,000 miles. they are the only zf rated place by all manufactures here in scotland. cost about 2-300 quid. you would have to google it up to see whos close to you.my xk is approaching 50,000 and i intend to have it done this year charlie