Just replaced my o-ring yesterday, on my 2004 xtype- thanks to the help of this web site- to my surprise - very simple, i did manage to brake a bolt- due to torquing to strong- but other then that easy- as for performance big difference the kitten response faster- & the reason I did the tune up was because I would get a hesitation when pressing down on the gas- Now at this moment no hesitation at all/ now i did reset the computer so ill be checking the codes soon- & keeping an eye on it but the feel is great- the O-rings that i put in was the updated ones from jaguar- so i keep you posted - hopefully that was the only issue- if you had the same issue please inform me how did u fix it -