I’m not always as good about changing all fluids on a used car as I have been in the past, it depends on the car. But this car definitely deserves it, especially being low miles and 18 years old with probably original fluid.
I decided to go with the following for fluids:
Oil: Castrol Syntec 5W-30. The manual recommends 5W-30. Although it doesn’t specifically call out synthetic from what I could find, I think given that this is the supercharged version it will have higher temperatures and probably benefit from it. Even naturally aspirated I would expect it to benefit as this does run higher temperatures than your typical American V8.
Rear differential: Going with Valvoline Synthetic 75W-140 gear oil. I know Jaguar has their specification on this for their special fluid. From some other posts I’ve found it seems like 75W-140 feels close in viscosity. Frankly for a rear differential I don’t get too worried about much other than 1) the oil actually being oil (as opposed to water) 2) it being relatively thick and 3) it having limited slip additive if required. It seems the XKR doesn’t have a limited slip differential, but the oil I bought does, which won’t hurt anything.
Transmission: When I was working on these cars when they were new, I don’t think this transmission was as well understood as it is now. Part of that was probably due to the fact that it was a transmission that hadn’t made it to as many Chrysler vehicles at that point. On my E55 I went with Valvoline MaxLife fluid (which claims to meet Mercedes-Benz NAG-1 fluid specification). This is commonly recommended on forums for Mercedes and Chryslers, and I’ve had success, so I bought 3 gallons worth and will be using that for my flush. I went with a CarQuest filter (which is good quality).
I’m not looking forward to changing the differential fluid, but having a lift will help.