As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE EN ROUTE FROM KOAK TO KTRM RESULTING IN AN AIR RETURN TO KOAK. RT HYD SYS OVER TEMP IN FLIGHT. EMERGENCY WAS NOT DECLARED, HOWEVER, THE AIRPORT ELECTED TO ROLL THE FIRE TRUCKS. LANDING & TAXI WERE UNEVENTFUL. R & R RT HYD TEMP TRANSDUCER.