3 points:
1. On 767/757, fuel densitometers are very moisture critical;
2. During our Fuel Leak simulator training, we demonstrated that the 767 was controllable with one wing FULL and one wing EMPTY.
3. The Flight Crew Training Manual (FCTM) states that the fuel imbalance limit is NOT for controllability reasons, but for long term structural reasons.
Sorry Mr Moderator, this belongs with #26 (757 fuel problem)