I have really enjoyed my recently (6 months ago) acquired 2005 xk8 conv.
The car had 110K miles on it and I had planned on handling all of the typical repairs as I was going to keep it a long time. After several months of loving it I decided that I would be better satisfied with a lower mileage xkr. This changed my repair and maintenance plans a lot. I did notice when I first drove the car the left rear wheel bearing clicked now and then...a thousand miles later I received my first fault 'abs'...over the following several thousand miles I received more and more various ones.
I had always suspected that the slop in the rear wheel movement had some relationship to the speed sensor and to the fault messages, well!!!
The bearing is now in bad enough shape that I have parked the car until I have time and energy to replace it. (purchased the bearing and nut last fall). The discovery I made last week was that when I push the car into a right turn the wheel bearing always clicks and I get one, two or more fault messages almost instantaneously.
This phenomenon is 100% repeatable with my car, at this time.
I guess I had better get going and pull it apart as spring time is coming.
also
If I have any fault messages that remain day after day I can (once again 100% repeatable) set off the panic mode, wait the 30 seconds it runs and then toggle the key fob for lock/unlock and all messages will not show their ugly little heads.
This car is really a driving delight and mental challenge.

wj

 

You might want to check the reluctor ring for the ABS, especially on the rear, driver side. It is a press fit on the rear axle/half shaft. On occasion, it gets loose and causes the transmission to complain. If you take the wheel off, the ring is under the sensor, where you would expect it to be. Alternatively, you can drive the car up on a ramp, and check from the bottom. Make sure the ring is SOLID with the axle. The ring is tucked in the wheel bearing area, but is plainly visible.

Best of luck, keep us posted.