I can find no documented evidence of a wing failure in a 172/152 other than from coming into contact with another aircraft mid air
Avgas 172,
My views are not based on accident data, they are based on really nasty corrosion I have seen in stripped down wings, in the leaves of the main spar, between the root fitting and the strut attach point.
Every one I have seen has had corrosion of varying degrees in this area, and this includes several aeroplanes that spent most of their life in "dry" conditions. In several cases, complete leaves were just dust, once the spar was opened up. It was not visible with the fuel tanks removed, and "tap" tests didn't reveal the extent of the damage.
It really says something for the actual strength of these aircraft, that there has NOT been a history of in-flight structural failure.