Looks really good, nice job. I wonder if anyone has done the same on the 06 onwards model? There is no obvious feed in the central cubby box as there is no phone. If anyone has I would be interested to know how.
If the level is correct and the warning persists, then the sensor must be at fault, that is not a code you would have to clear. New sensors are relatively inexpensive and I think a pretty easy DIY fix.
Agree with Andy, aftermarket parts fine for most jobs, but transmission oil must be the proper stuff, though you can still get cheaper than £300. It will exasperate you at times, but when it's running well nothing finer!
Does the noise persist when driving? Most knocks are suspension or wheel bearing, the latter may be a more constant grinding noise. First thing is to remove the wheel and check for any obvious suspension issues. Difficult to assess wheel bearings as the usual method of looking for play when rocking ...