Hi @Dieselpete
The water pump is an easy spot - apparently.
The steering rack issue - not so easy. Difficult to say how many owners have encountered the issue. I saw plenty of people on the US forum with quotes similar to "Mine sometimes does that.". So, it is possible that there are more examples out there than we are aware of. Lets also not forget that the exact symptoms have been reported on other Toyota's. It is a recognised issue via a Lexus Service Bulletin (Google L-SB-0016-11). So, if it did occur, I'm not sure if you could push Lexus - even out of warranty?
The £3.5K was what the dealer told me it costs for the rack to be replaced. How accurate this is, I don't know. I'm also guessing that if you got the rack fitted by a non Lexus dealer, then the price would be significantly less?
Thats what I know.
If I was a betting man (which I am not), you'd have to look at the percentages. Including mine, I've heard of one other that needed the rack replaced. So, what's that, less than 1%?
I know the IS-F is so much more reliable than the competition. In fact it is more reliable than most cars, but as you said, it was a £50k+ car new. That's why when I bought mine, I was less worried about getting a deal, but happy I managed to get 3 years warranty :)