What was found
PILOT REPORTED DURING CLIMBOUT, LT "DUCT LEAK" LIGHT ILLUMINATED. LT BLEED AIR WAS SHUTOFF. AFTER 3 MINUTES LIGHT NEVER EXTINGUISHED. LT ENGINE WAS SHUTDOWN, DECLARED AN EMERGENCY, RETURNED TO DEPARTURE AND LANDED WITHOUT INCIDENT. FOUND THE SEAL FOR OVERBOARD EXHAUST RECEIVER ON THE LT DE-ICE PRESSURE REGULATOR BLOWN OUT ALLOWING THE HOT EXHAUST AIR INTO THE L/E FAIRING CAUSING THE LT DUCT LIGHT TO ILLUMINATE. PRESSURIZED LT DE-ICING SYS FOUND THAT THE PRESSURE REGULATOR, PN 38E96-5A WAS ALLOWING TOO MUCH EXHAUST AIR INTO THE RECEIVER CAUSING THE SEAL TO BLOW OUT. R & R THE LT DE-ICE PRESSURE REGULATOR. GROUND RUN LEFT ENGINE OPS CHECKED NORMAL.