Is this still the preferred source for the transmission pan/sleeve/fluid replacement kit in the USA:

http://www.thectsc.com/products/oil-change-kit-for-bmw-hyundai-jaguar-land-rover-rolls-royce-186-50.html

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My karma just ran over your dogma
'08 Jaguar S-Type 4.2 "Satin Edition" (250.06 hp / 259.67 torque)

 

If your question is based on availability, pricing and level of service, I have found California Transmission Supply to be a very good source for ZF gearbox information and parts.

 

Turns out there is an alternative:

SNG Barratt - The Ultimate Jaguar Parts Specialist

But it costs more ($340.00 v.s., $258.19).
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Jaguar: Grace, Pace, and Space - Sir William Lyons
'08 Jaguar S-Type 4.2 "Satin Edition" (250.06 hp / 259.67 torque)

 

Maybe it's just my Scottishness, but that doesn't appear to be a feasible alternative.

 

EBay had some good prices on "kits" as well. I looked about 2 weeks ago.