I could sell you a good pair of winglets for it, but unfortunately EASA would not be very happy if you installed them.

The first thing I'd do is make sure that cockpit ventilation air has somewhere to escape the fuselage. There is probably a path through the aft fuselage to a vent at the base of the rudder. Make sure that it is not blocked.

Next, I'd check to make sure that air cannot pass between the fuselage and the wings. If air can get drawn into the wing at the root ribs and out through the control connections at the ailerons, it can waste a lot of energy. Check to make sure the controls are sealed at the root ribs.

After doing those, then I'd work on the canopy seal and control surface hinge seals.

--Bob K.