Seeing as the thread topic is AYC, though I am not sure the first post is related to it...
My first AYC bar keeps lighting up sometimes on straight flat road, then going out. It stays on sometimes for 5 seconds, sometimes 10. Just give it a service to clear it up? And also, where are the sensors for the AYC? Could one be dodgy?
as long as they are the same left and right, and within a few mm of tread all round, you should be fine. If the tyres at either end have significantly less tread than the others you will cause problems for the centre diff, and if there is any difference between the left and the right, you'll have AYC problems.