I have a 2011 Z6 and the forum was full of complaints about them pulling hard right with single cable steering. I got mine pretty good in the end but still torqued abit until the trim was perfect and sitting up on the pad.
I bit the bullet about 2 months ago and bought a Baystar Hydraulic steering system and installed it home and absolutley love it. The learning from installing was, you can't get the standard Z6 cable out without cutting it, so don't waste your time like me unbolting motors to get the cable out of tube onlt find you cant get it out of the hole in hull under the dash anyway. Just cut it, save 2 hours and move on.
The rest is pretty easy. you will need make the hole in the dash a little bigger for the helm with a hole saw, everything else is fine, your old steering wheel fits, all the hardware and fittings are supplied as is the fluid.
The amount of turns lock to lock will increase so steering response is not as rapid, there is no feedback or torque at all and you can let go at any speed.
I say go for it and you'll be a happy camper.
