As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED SHORT DURATION SMOKE IN COCKPIT. RETURNED TO ORIGINATION POINT AND MADE A NORMAL LANDING. AIRCRAFT WAS TURNED OVER TO MAINTENANCE AND IT WAS DETERMINED THAT HYDRAULIC RESERVOIR SIGHT TUBE HAD FAILED AND RESERVOIR PARTIALLY DEPLETED. CAUSE OF FAILURE APPEARS TO EXCESSIVE HEAT DAMAGE. CAUSE OF DAMAGE IS UNDER INVESTIGATION. PRESENTLY UNDER WAY.