As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CLT - DURING MAINTENANCE TEST FLIGHT FOR Q5 CHECK, STRONG FUMES FORWARD OF FIRST CLASS WERE REPORTED AS TAKEOFF THRUST WAS SET. FUMES WERE THAT OF A MUSTY SMELL. TURNED LEFT PACK OFF AND RETURNED TO CLT. FUMES CONTINUED UNTIL TOUCHDOWN. OPENED WINDOWS ONCE ON GROUND. MAINTENANCE BOROSCOPED THE NR 1 ENGINE AND FOUND AN INTERNAL OIL LEAK AT THE NR 3 AIR/OIL SEAL. REMOVED AND REPLACED NR 1 ENGINE ASSEMBLY.