[jagarra]

I agree that the starter may need a new Bendix gear set up. It seems that the starter gear is not getting enough travel to engage the ring gear. Possible causes are bad Bendix, worn or bent yoke that drives the Bendix into the flywheel, also check it's pivot point for wear. The bushing at the nose of the housing could be missing or so worn that the Bendix is too low to hit ring gear. Check all the components that move the bendix assy forward, some part there may be the fault.

A possible source for parts is rockauto.com, they carry items for these trucks, not sure about overseas shipping.