What was found
GROOVES WORN IN ROCKER BOX OIL RETURN TUBE. AUXILLIARY HEAT AIR DUCT AT LOWER SIDE OF NR 1 CYL WAS RUBBING ON OIL RETURN TUBE. GROOVES APPEARED TO BE 30 PERCENT TO 50 PERCENT THROUGH TUBE. AIRPLANE WAS 2.2 HOURS TIME IN SERVICE AFTER ANNUAL / 100 HOUR INSPECTION. HEAT DUCT HAS TO BE CRUSHED TO FIT THIS INSTALLATION. THERE IS INADEQUATE ISOLATION BETWEEN DUCT AND ENGINE CYLINDER LUBRICATING OIL RETURN TUBE.