PTU. SERVICE LETTER RECOMMENDED 10-DEC-2013 MOS SI. 737-SL-29-121 INCORRECT ORIENTATION OF POWER TRANSFER UNIT (PTU) RECOMMENDED 03-APR-20I4 PRESSURE FILTER ASSEMBLY. SERVICE LETTER MOS SL 737-SL-30-017 COWL THERMAL ANT-ICE VALVE IMPROVEMENT. SERVICE LETTER INFORMATIONAL 13-OCT-2000 MOS - (s) SL 737-SL-3