Hi Darren, just been reading about your front wheel bearing, this is quite common on the Sierra and as has been said a small amount of play is acceptable in regards to your MOT. I have the same situation on my own 2WD Saph the N/S/F bearing has been like this for at least 5 years and has never got any worse despite covering thousands of miles of hard driving. Whilst it is running quietly I would leave well alone.

CheeRS, Mike