Heavy aileron trim during cruise...
I have seen and troubleshot this defect to return a couple defects on the 767. After checking the usual suspects such as cable/actuator rigging to reveal to nil out of rig the following has been discovered on different aircraft for same excess aileron trim defect..
1st and the most common, Rudder trim indicator "ribbon" stretched and not indicating centre (0 units ) when the rudder is in the neutral position.
I have seen a few tech write ups of excessive aileron trim to trim out the rudder displacement due trim indicator. A bit of tail chasing. The EICAS flight control position indicating is not accurate enough to show the rudder out of trim especially in the high speed mode. I have often mused that we must have quite a few pilots with different length legs..
Its quite common to see up to 2 units of rudder trim on the 767-300 during climb and early cruise , then use same amount of trim in the opposite direction on descent. It would appear a faulty rudder trim indicator could trip up crews in a busy (high load) cockpit as aileron trim is used to achieve the aircraft to fly straight and true.
The 2nd and less common is due to Trailing edge flap rigging /construction.
There was a time when the out board flap assy were being changed frequently due to a mod or water ingress and being swapped from aircraft to aircraft within my fleet causing same trim defect .
For aircraft that need excess aileron trim to fly level with all rigging of flight controls checked ok. The maintenance manual states an amount of shim material to fit Vs the amount of aileron trim to lower the outboard flap assy (one side). This does not lower the flap the same as extension of the flaps but lowers the whole assy down away from its mounts...
Not saying this was the reason for the aileron displacement in the original posters question just something to add to the speculation