What was found
DURING TROUBLESHOOTING OF AN OIL LEAK ON ACFT, A CRACK WAS FOUND IN THE UPPER LT WHEELWELL, ABOVE THE LANDING GEAR FENDER. FOUND 3 ADDITIONAL CRACKS IN THE LT WHEELWELL SIDE WALL STRUCTURE LIGHTENING HOLE. ALL 4 CORNERS OF LIGHTENING HOLE WERE CRACKED. THE LOWER FWD CORNER IS CRACKED THROUGH THE OUTER AND INNER DOUBLERS AND YOU CAN VISUALLY SEE SEPARATION. THE OTHER 3 CORNERS ARE CRACKED BUT NOT TO THE SAME DEGREE AS THE FIRST. SIMILAR CRACKS FOUND IN THE RT MAIN GEAR WELL ALSO. INSP OF 14 ADDITIONAL ACFT FOUND CRACKS ON 6 ACFT. CAUSE OF CRACKING IS UNDETERMINED, HOWEVER THESE ACFT HAVE HIGH USAGE AS TRAINERS. ADDITIONALLY, PROP BALANCE ISSUES MAY ALSO BE A CONTRIBUTING FACTOR.