Is it possible that at least part of the damage is not landing related at all? Dropping the gear or raising it at high air speed puts undue stress on the gear similar to hard landings and since the gear tends to retract asymmetrically that could explain the damage on one strut but not the other. Also, this aircraft has a manually triggered hydraulic pump, is it possible to overstress the gear if you run that motor while the gear is locked? Not questioning anyone's technique, just asking if it's possible.
Aside from what has already been discussed, one additional thing that might be causing a single gear issue would be attempting a tight turn on the ground with brake on the inside of the turn without forward motion on the inside main wheel.
This is a problem in real tail wheel airplanes and simply involves taxi technique. There MUST be forward motion on the mains BEFORE brake is used on an inside wheel to tighten a turn on the ground. Failure to have this forward motion in play when turning will indeed place a HUGE stress on the inside wheel and strut as the aircraft pivots on that strut and it becomes the center point for the attempted turn.
One more thought. Just got off the phone with Scott. He suggested the issue might be associated with slewing if that is involved. If for any reason. There is a HUGE amount of drag associated with gear retraction and extension in the P40 specifically because the wheel pivots to a dead on planform face during the process, so the maximum gear speed can be a real player stress wise if for any reason the process is initiated over Vg.
Hope all this helps a bit.
Very good points and I know I've been guilty of the pivoting on the gear without forward motion.