I have seen Piper aircraft that exhibit consistent wing drop for two reasons both of which are hard to see.
The first one was a Piper Seminole that the front wing attach spar bushing which is a press fit into the forward attach tab and that goes through 2 steel plates in the fuselage had been dislodged . The bushing is not clamped between the plates and can be dislodged from the fitting causing the leading edge to change angle of incidence by a couple degrees even with the main spar and rear fitting bolts correctly installed .You won't see it on less the aircraft is jacked up and you lift up the leading edge .The one my workmate found had cut about a third of the way through the bolt.the bushing can be seen by taking out the sidewalls in the cockpit forward of the seats .
The second cause is some one pushing on the Ailerons to move the aircraft which evan when you can't see the deformation by eye makes a difference that can't be rigged out. The only way to check is to swap in a known serviceable aileron and test fly.
This is specifically mentioned in the maintenance manuals.