minnieapolis g900 hydraulic leak

[DUSTINBAYS]

This is my first post on here so hello from Texas...

I have a Minnie Mo g900 that is somehow leaking into the differential. Its a closed circuit hydraulic system. We have pulled the rockshaft system off and cleaned the plate between the hydraulic housing and the differential but have found no cracks. the gaskets looked to be ok and in position. There were no leaks to the outside of the housing at all. There's no hydraulic fluid in the engine oil or the coolant and the Diff shows to be overfull. I'm lost on where to go next.. any ideas would defiantly be helpful. Also, is there any place I can order the new gaskets for the hydraulic to diff plate.