What was found
ON TAKE OFF RIGHT AFTER GEAR RETRACTION, FORWARD FLIGHT ATTENDANTS REPORTED L1 DOOR HAD A GAP WITH A LOT OF WIND NOISE, FLIGHT ATTENDANTS REPORTED SEEING DAYLIGHT. ACFT GROUNDED. AIR TURNBACK, FOUND LOWER ENTRY DOOR FLAPPER SEAL NOT SEATED PROPERLY TO L-1 DOOR. ADJUSTED FLAPPER SEAL TO CORRECT POSITION AND CLEANED AWAY DEBRIS AND LUBED FLAPPER SEAL SPRING IAW AMM 52-11-00-420. PRESSURIZED A/C WITH APU TO 6 PSI DIFF, NO DEFECTS NOTED, OPS CHECK NORMAL IAW AMM 36-00-00-860.