You say that "his aircraft was repaired by grafting on a section of replacement wing" but I would have expected it far more likely (having lost the outboard 10ft) that the entire outboard wing (from just outboard of the engine) was replaced with a new one. Given that it was then flown once satisfactorily, it is unlikely that the same wing then fell off on the next trip implying a poor fitment (although I know anything is possible!). It is entirely probable that the reason the replaced wing is not mentioned in the accident report is because it was the other side and so was irrelevant.