Oldskewel no worries my major worry of having mismatched tires and possible transfer case issues is over at least after tire change although I managed to scuff a front tire wall on kerb maybe total surface 1sqaure inch no rip or tear or threads but a 1mmm layer off the rubber outer wall no strands exposed or wire(yet)!!!!!, as for your points here is what I have and I guess a video would be best to show ya my dead zone? in response to your findings:

I have a 1cm rotational motion of the steering wheel about its normal axis, I reckon. As for it being a dead zone currently can't tell if anything is going on steering rack when I wiggle it 1cm left or right.

With engine off, steering unlocked, parked, etc. ... I can rotate the wheel to the right, let go and the wheel goes back to its original centred spot (if I have parked wheels straight), same for rotating to the left it goes back to where it was(mus be the spring-like compliance?). I'll get a video i reckon, only way, then can see if this could be the reason for my 60 and over wobble....as for getting to from the top, dunno the 3.0d has some pain in the bum features like the air filter replacement needing alot of parts removing so I will wait for other 3.0d owners to chime in....

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E53 X5 3.0d SUV prod.date 11/2004 eng.variant M57N Europe Right hand drive N