What was found
AIRCRAFT WAS GROUNDED: EMERGENCY RETURN DFW FOR BURNING WAX SMELL ON FLIGHT DECK. EYE AND THROAT IRRITATION FOR BOTH CREW MEMBERS. NOTICED AS POWER WAS APPLIED ON TAKEOFF AND PERSISTED THROUGHOUT THE 40 MIN FLIGHT UNTIL ENGINE SHUTDOWN. NO SMOKE, BUT ACRID, WAXY ODOR. AIRCRAFT WAS OVERWEIGHT. FLIGHT LANDED WITHOUT ISSUE AND TAXIED TO THE GATE. MAINTENANCE FOUND GEARBOX O-RING ON FULE PUMP TO BE BROKEN AND LEAKING. MAINTENANCE REPLACED APU FULE FILTER & O-RING.