As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE SITTING AT THE GATE WITH THE APU & PACKS RUNNING, WE GOT SMOKE IN THE CABIN. AFTER SHUTTING DOWN THE APU, THE SMOKE CLEARED. UPON INSPECTION OF APU, FOUND OIL LEAKING FROM EXHAUST. REF ITEM NR 3 BELOW THIS LOG PAGE FOR CORRECTIVE ACTION.