Hi, I have a 2.7 S type SE Automatic year 2006 with 155,000 miles on the clock. The most important is that any machine can only be as good as the service it was given. This is the important since there are no major problems really. This engine is proven tried and tested in range rovers, citroens, ford cars and needless to say, Jaguar tuned it up even further - its a beauty really. So the one I have was purchased by from the UK (I live in Malta) when it had 122,000 miles on the clock. Why did I by this one. Because it belonged to a medical specialist (one onwner) that always serviced the car regularly at a main dealer and that means that all problems, if any, had been ironed out. But most important (since ultimately, its easy to change the engine ) This one had original spray, impeccable as new interior, no rust at all, and everything looking and functioning as if it were new. Dealing with such issues as rust and climate control and all the rest of it is expensive and could be a time consuming drive without a finish. So buy a well looked after car. I know I paid some 2000 more for it, but I have no regrets. Its a really well looked after car.
Other than this I can assure you that if the 2.7 diesel engine is serviced on time, and as recommended by Jaguar using original consumption parts and the right Oil which is most important for any diesel engine and turbo, you will have no problems at all.
It is a damm reliable car and the torque of the engine couples to its gearbox especially if you switch it to sport mode is out of this world and a pleasure to experience.
Go for it. Just make sure you buy one that was well looked after and has a proven history of being serviced by Jaguar authorised service centre (not dealer- some dealers are not authorised to service them).
Rust. Look under the door sills. Its not easy to see since it is covered with a neat plastic cover. The under body is also mostly covered completely with a plastic cover underneath which, I found a large radiator which I then learned that it is a fuel cooler.
So you have to jack up the car, for sure, to really know.
Some surface rust in the sills or underbody can be easily resolved. BUT if rust in the sills / running board, has eaten parts of it away and in some cases, was allowed to go up to the A and B pillars to which the doors etc are anchored - just get out of there soonest possible.
This is what you need to watch out for !
Hope this helps - ask anything - and Good luck too.