I havent got a definitive answer I am afraid but some suggestions!
There a few other things you could consider, if you have exhausted all the ITBS treatment (all of which i am sure someone will tell me is wrong, so take them with a pinch of salt! - i am not an expert!)
the first thing is, it could be your thigh muscle itself, not the ITB - check out this webpage on trigger points
http://www.triggerpoints.net/triggerpoints/vastus-lasterallis.htm
another thing is, it could be you are hitting the ground hard, consider if you heel strike or forefoot strike, you might like to consider a change to a more forefoot strike as in a barefoot running technique (i only mention this as I overpronate on my left leg and find barefoot shoes and accompanying technique very good)
the next thing to consider is that it is simply that your left leg is weaker, you are running 'off centre', or it is something that cannot simply be fixed by doing all the accepted cures (eg, stress from expecting the leg to hurt is causing you to tense up and making it worse? - my husband gets a bad back when he gets stressed!), also have you been to a doctor about it, there could be a different sort of problem internally?
of course it could be something else you are doing that is not helping - eg I myself have had intermittent problems with the inside of my left knee, which at first i put down to overpronation, then unruly thigh muscles, then when I thought about it i realised it was worse whenever i increased my strength training which includes doing squats. I am considering that it may be just due to being 48 and having a knee what is getting old and crunchy so i am in the process of leaving out the squats and trying other quad strengthening exercises instead (whatch this space!) so are you doing something else your leg does not 'like'
sorry for the waffle but the point i am trying to make is that it is not always as simple as putting a label on it and picking the 'correct' solution (which i am sure you have realised!) Take a holistic view and consider other forces that could be involved?