As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE GARLOCK SEAL OR LIPPED SEAL ON THE AIR CONDITIONER PULLEY SHAFT WHICH STICKS OUT THE AFT SIDE OF THE STARTER ADAPTER (THE SHAFT WITH THE CASTELATTED NUT AND COTTER PIN ON THE AFT FORWARD OF IT), WAS LEAKING OIL. HARD TO LOCATE LEAK AT THIS SEAL AS IT LOOKS DRY ALL THE TIME. HAVE FOUND MANY IO520 AND IO550'S LEAKING AT THIS SEAL. SEAL REPLACEMENT STOPS THE LEAK.