What was found
FLT 251 OAK-LGB, HYD G RSVR LO PR ON DESCENT PASSING FL 270 AND LOSS OF GREEN HYDRAULIC SYSTEM. REMOVED AND INSTALLED NEW O-RING ON NR 1 ENGINE PUMP PRESSURE SWITCH PER 29-11-17-40. SERVICED HYD, RAN NR 1 ENGINE, NO LEAKS NOTED. A/C OK FOR SERVICE.