What was found
AT FL390 A LOUD HISSING/ WHISTLE SOUND WAS HEARD FROM MAIN CABIN DOOR. IT COULD BE HEARD BY BOTH CREW & PAX. UPON INVESTIGATING NOISE, SOME AIR WAS FELT COMING IN FROM RT FWD CORNER OF DOOR. NO DOOR ANNUNCIATORS OR PRESSURIZATION ISSUES. NOISE APPEARED TO DECREASE IN DECENT BELOW FL 200. ON POST FLT, A TINY SLIT CAN BE SEEN ON FWD SEAL. REMOVED DAMAGED FORWARD LOWER SEAL & INSTALLED NEW SEAL IAW MM 52-10-04. REMOVED DAMAGED UPPER SEAL & INSTALLED NEW SEAL IAW MM 52-10-04. REMOVED DAMAGED LOWER AFT SEAL & INSTALLED NEW SEAL . PERFORMED CABIN PRESSURIZATION WITH APU IAW MM 21-30-00. NOTED NO NOISES OR LEAKS COMING FROM MAIN DOOR. PERFORMED LEAK CHK OF SERVICE AIR LINES TO TEE FITTINGS WITH NO LEAKS NOTED.