After the somewhat grueling procedure (recently reported) with the object of stopping the transmission shifting squeak, I am happy (and relieved) to report that the use of new fluid - Mercon SP (7 quarts) - appears to have solved the problem. I can detect no trace of the noise. The fact that a change of about 3/4 of the volume would immediately silence that squeak (call it what you will) is nothing short of amazing. According to ZF and Jaguar, a year from now I'll be wishing I had used Lifeguard 6, but right now I see no reason to be concerned, with my infinitely cheaper, equal-spec' Mercon SP, a-la Ford.
Also, I would be remiss not to offer gratitude to the members who have written on the subject, and those who have written on the substitution of Mercon SP. Thank you!

 

Glad to hear your problem has been sorted and you are happy. Lets hope it stays that way.
I used the ZF fluid in mine, there is no way I am quibbling over a few bucks when a $4000 transmission is at stake!

 

Running Mercon SP in these ZF 6HP26 transmissions is a no-brainer. Both of our Jaguars run it with zero issues. In fact, my 2005 S-Type 3.0 shifts better and smoother today at 96,800 miles than it did when I purchased it at 18,000 miles with its factory fill of Lifeguard 6 back in December 2008....

 

I'd say chemistry counts more than branding.

 

And on my list Peace Of Mind counts the highest!

 

Hey Atlastajag1 what mileage did you change yours? Mines probably original at 26K.. it's got me thinking maybe it wouldn't hurt to change..

glad yours is working out!

 

Ford, which manufactures this transmission under license from ZF, recommends 150,000 mile drain and fill intervals with Mercon SP. After chemistry I would trust engineers over branding or emotion.

Not lifetime but pretty close.