What was found
AIRCRAFT WAS GROUNDED: ON CLIMB OUT, BELOW FL150, VERY STRONG ODOR IN CABIN. DURING CRUISE, THE ODOR WENT AWAY. ON DESCENT, BELOW FL150 VERY STRONG ODOR RETURNED AS A PLASTIC & SOUR SMELL. THE FLIGHTDECK COULD SMELL ON DESCENT AS WELL.MEL AUTHORIZED. ACCOMPLISH JOB CARD 26L00021001 DRAIN OIL #2 ENGINE TO PROPER LEVEL. ACCOMPLISHED JOB CARD 26L00021003, 26L00021004 NO ODOR FOUND AND AIRCRAFT OKAY OR SERVICE.