The tensioner problem was fixed on the 2013 5 liter. Was not a problem on either the few 4.2s from 05 or later 4.4s in the LR3s.
The 4.0 Jag V8, prior to US MY 2003, had plastic secondary tensioners that often split. About $3000 to fix unless you were real handy, then only $120 for new metal tensioners. Took me a couple of hours to replace my secondaries on my last X308 Jag. The 5.0 liter replacement is far more complicated: lots of threads on this, Jag, and Range Rover forums.
But if I were to guess, the price differential is due to last V8 as standard. . . and a year newer. My practical experience with Jags and LRs has been that the last year of any model run has a distinct advantage of having most of the "issues" resolved.
