Since you appear to have a good relationship with the XK owner, find out what repairs were performed over the last 11 years. Get under the car and inspect the suspension for worn bushings. If you don’t know how to do that then pay for the car to be evaluated at your local Jaguar dealer.

You are considering a 4.2 litre car, so the water pump is a non-issue. The suspension bits mentioned in the $7000 bill were replaced under a warranty...in which typically everything and anything that would show normal age/mileage-related wear would be replaced, and done a maximum billable cost. This is not an indicator of *needed* replacement cost. Yes, suspension components wear with age and use (this happens to any car...and if you had the Nissan examined for wear in the suspension, there would suddenly be parts that needed to be replaced!). There is no "poor design" in Jaguar suspensions. There is design which optimises a balance of performance and refinement, and maintaining that refinement is what can sometimes indicate a replacement. Jaguar has always been a leader in suspension design.

Whar we are trying to tell you, from experience (and I have owned 32 Jaguars - some of them for as long as 12 years) is that the cars, especially the XK under consideration, are very reliable (assuming proper maintenance)... yes, the XK is/was an expensive car -but it is not unreliable (you seem to assume that it is). At the other end of the Jaguar price spectrum was the AWD X-Type, of which we have owned 3 - we have 2 at present in long-term ownership, used daily. My wife's is a manual shift model, driven daily for every sort of use, outside 24 hours a day, for now 15 years, ...the sum total of repairs? An oxygen sensor, a nylon gear on one of the seat motors, and most recently, the water pump...three repairs, all minor, in 15 years. So much for the "Jaguars are unreliable" myth. But as with every and any car, the service history and general condition are everything. A Bentley, badly maintained, will also be unreliable...

Dont do an even trade. Your Nissan is a racerboy car and the Jag is not. I have a 2007 with over 100k miles and the only thing that has pissed me off is the price of a new alternator. $800 for a Denso part. I recently replaced 2 Remanned Bosch models because the bearings went out on them. So I had no choice but to get a factory replacement. Bushings go out. Other than that theyre not a pain. If youre in your 70s and worried about reliability, time to stop worrying and start living smart. An XK is a smart buy when done right. People will always think youre paying too much, or making too much. The 370 is cool and Id drive one, but nah... its just not special

Good move. Go for a 2 hr drive with the Jag before you buy. Give him $40, a six pack and go driving, just to test everything out. Stay away from dealers, and get yourself in touch with a good local shop. Get your oil and filter from NAPA and drop everything off. Its not as special as it looks. Standard drivetrain and sexy sheet metal are what make it special though.

5 years newer, updated taillights, updated headlights, 85 more HP, for only $5k? Sounds like a nobrainer to me.

But you need to see and drive both. They don’t look the same, they don’t sound the same, they won’t drive the same.
Does either car ‘speak to you’? Push all the right buttons?

When Jag made the 2007. It was actually made to be reliable. But then they got fancy with it and decided to engineer a couple of weaknesess into it, just to give it that old jag feeling again. Just kidding, but the problem I see with 5.0 cars is the lack of a dipstick, and the waterpump design. Different animal. The bite is also different😁