Hitachi ZW 550-6 Operator's Manual page 308

17. One point each to front and rear axle seal (24).
--- every 1000 hours
 Remove breather nipple (25).
 Fill grease from grease nipple (24) until it spills out of
breather nipple (25) hole.
 Wipe the spilled grease and install breather nipple
(25).
f
NOTE: Breather nipple (25) is located on the top, opposite
position of grease nipple (24).
MAINTENANCE
Front axle
7-24
25
24
24
Rear axle
MNHE-07-016
MNHE-07-013