What does your arsenal consist of? It'd be helpful to know what you've tried first...

My gut says if you've tried all the usual suspects, then try wet-sanding with 1000 grit till the yellow goes away... then up to 2000 grit and polish...

My only concern is that the yellow stain is actually on the aluminum and moister got behind the clear... if that's the case, then you'll have to get down to metal to clean it up then re-coat with clear...