As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE FLIGHT, NOTICED HIGH MAIN TRANSMISSION TEMPERATURE. AT THAT TIME MY PASSENGER IN THE BACK SEAT INFORMED ME THAT HE COULD DETECT AN OIL BURNING ODOR. TURNED ACFT AROUND AND RETURNED TO DEPARTURE. MX DRAINED A LITTLE MORE THAN A QUART FROM THE TRANSMISSION DUE TO OVER SERVICE. TOOK OFF FOR MX TEST FLIGHT, PROBLEM WAS RESOLVED. (K)