It is an accepted fact that the later six-speed automatic transmission (ZF) in, for example, the diesel S-Type, requires a very specific ATF, Lifeguard being seen as the best and substitutes such as Mannol being seen by some as acceptable, but NEVER... NEVER, standard ATF.
My point for discussion is this:-
I know of a diesel S-Type (not mine) that had the transmission filled with standard ATF (Dexron 3 or equivalent) and has since been driven 10 000 miles without a problem.
Over to you