David,
Sounds like the fix is well in hand, but did you find the root cause?
It might be worth checking the inboard end of the wing stay for witness marks to ensure that it's not fouling on the upper kingpin washer. The stay angles do vary between cars and my offside wing stay on the '12 4/4 fouled as described. Over time, this would transmit jolts along the stay sufficient to fatique the wing.
Apologies if this is stating the obvious..
