DURING INSPECTION OF A LUBRICATING SYSTEM, THE CONTRACTOR STEPPED FROM THE FRONT FRAME ONTO WALKWAY AROUND THE CAB. THE CONT. BUMPED INTO THE MIRROR ON THE RIGHT HAND SIDE OF THE MACHINE, LOST HIS BALANCE & FELL APPROX. 13' TO THE GROUND. THE MACHINE WAS IN A PARTIAL STATE OF ASSEMBLY & HAD NOT BEEN PLACED INTO SERVICE.