Employee was replacing an axle shaft of Komatsu HD1500-7 Water Truck. Employee found the axle bushing was stuck and used a glove hand to attempt to lift the sun gear side of the axle to free it. Upon pushing upwards on the sun gear, the employee lost grip on the oily surface and EE's forearm contacted a spline on the sun gear resulting in a 1.5"" laceration requiring 5 stitches.