As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BURNT SMELL NOTICED BY CREW ON CLIMB OUT. ALL INSTRUMENTS INDICATED GREEN, NO SMOKE OR FLAMES NOTICED. FIRST OFFICER COMMENTED HE MAY NOT HAVE SECURED THE OIL FILLER CAP. OIL PRESSURE STARTED TO FLUCTUATE AND THE DECISION WAS MADE TO RETURN TO THE DEPARTING STATION. UPON LANDING IT WAS DISCOVERED THAT THE CAP INDEED WAS NOT PROPERLY SECURED. NOT PARTS WERE FAULTY AS THIS DIFFICULTY WAS CAUSED BY THE CREW