As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOTS REPORTED AN ODOR IN THE CABIN AND COCKPIT WHEN THE PACKS WERE SELECTED ON WHILE USING APU BLEED AIR. TROUBLESHOOTING REVEALED THE APU COMPRESSOR CARBON SEAL WAS FAULTY, ALLOWING OIL TO ENTER THE AIR SIDE OF THE APU AND SUBSEQUENTLY THE ACM AND CABIN AIR SYSTEM. THE AIRPLANE WAS MOVED TO THE SAVANNAH SERVICE CENTER FOR APU REPLACEMENT. GULFSTREAM INFORMED US THAT THIS IS A COMMON ISSUE WITH THE HONEYWELL GTCP 36-150 MODEL APUS.