Level flight requires slight right hand turn input

[B2C2]

Since I purchased my 1969 T337D about 4 years ago, I have had a need to put in a slight amount of right aileron deflection for straight line flight. The amount of aileron deflection needed is about 1/4-3/8 inch as measured by looking at where the aileron is w/respect to the wing tip, or about 5-10 degrees of right turn in the yoke. I have played around with using rudder trim and also the aileron trim tabs to compensate for this but there isn't enough adjustment there to center the yoke in flight. With the right turn in there from the ailerons and no rudder trim deflection the ball is pretty well centered and the plane makes book numbers for speed. It has a Robertson kit installed as well. I was wondering if anyone else has seen this behavior and if so is there a way to address it? It's not a critical problem but kind of bothers me that the yoke isn't centered and the ailerons faired with the wing tips and flaps in level flight.