cpt,
The change in 4P should be easy to measure, get involved with the maintenance guys when they rig the accelerometers. The pilot's seat track outboard vertical tells most of the story. The centerline vertical (center console) tells the rest.Most likely, it is the bifilar, which sometimes gets dirty and caked up.
The thing most pilots miss is that nothing about the blade track will make 4P, and nothing that you do to the track will make it go away. The 4P is a natural product of the rotor, and also comes from the main rotor wake hitting the horizontal tail (try 1/2 ball of left and then right sideslip at 145 knots to see how much the position of the tail relative to the wake affects 4P in the cockpit.)