Many thanks, as ever, for all the useful advice.
The great thing is that the above suggestions are based on experience and evidence, not just opinions.
My policy with my Japanese import P38 4.0SE is that I replace (within reason) items that are critical even though they might be OK, continuing on a known firm base, so to speak.
My 90k miles car has an extensive service history, but all in hand-written Kanji on meaningless little diagrams. Very pretty, but totally impenetrable.
So on that basis I plan to replace the fan viscous coupling, and I note that Febi Bilstein make one. Although more expensive, it lacks Britpart's Russian roulette feature....