611-XXXA CODE O-RING STATIC SEALS - HYDRAULIC FLUID EXTERNAL LEAKAGE AT LOW TEMPERATURES. SERVICE LETTER MOS 21-MAR-2006 SL 737-SL-20-048 REV. 8 NAS1611-XXXA CODE O-RING STATIC SEALS - HYDRAULIC FLUID EXTERNAL LEAKAGE AT LOW TEMPERATURES. SERVICE LETTER MOS 22-SEP-2006 SL 737-SL-20-048 REV. C NAS1611-