What was found
LARGE BLACK STREAKS ON UNDERSIDE OF AIRCRAFT, STREAKS ARE TACKY TO TOUCH AND HAVE NO NOTICABLE ODOR OR COLOR OF ANY AIRCRAFT FLUIDS. APPEAR TO ORIGINATE FROM WHEEL WELL AREA. OPERATED BOTH HYD. ACMP, FOUND NO ACTIVE LEAKS, DRIPS, PUDDLES, OR POOLING. HYD. SYSTEM FULLY SERVICED WHEN ACFT ARRIVED AND LEVEL DID NOT LOWER. SUSPECT BLACK STREAKS ARE RESIDUAL. OPERATED BOTH HYD. ACMP AND CYCLED THURST REVERSERS, AILERONS, AND FLAPS SEVERAL CYCLES. UNABLE TO FIND ANY LEAKS AT THIS TIME. CARRIED AS EXTERNAL WASH APPROVED. CARRIED.