D46U straight blade,D46U cat angle blade,allis chalmers AD4 grader and Khoering 404 dragline. D4C 40A,D4 2T and scraper.
i am by far inexperienced on this problem but i would use diesel first.
One thing to remember is whatever you put into the steering clutch compartments can easily pass into the adjacent oil filled compartments on these old machines. I have experienced water migration through pto shaft seals that were not leaking oil OUT, when the seal was immersed in water a few inches while the pto was turning So don't put in more than enough to have the clutches dip into it when they are rotating. There is nothing to be gained by filling them higher and potentially lots to be lost.
I would stick to petroleum solvents like kerosene and diesel. If you wanted to get fancy, a parts washer solvent would probably work well.
I would proceed under the assumption that this washing process will result in a nice cleaning in preparation for the eventual removal and repair of the clutch. AND I WOULD CAREFULLY CHECK THE FREE TRAVEL OF THE CLUTCH LEVERS AND THAT THERE ARE NO FOREIGN OBJECTS BLOCKING THE LEVER FROM RETURNING FULLY FORWARD.
GOOD LUCK
remove the brake adjustment bolt on the bottom of the housing or you will leave a fair amount of fluid in there when you are "flushing". you can remove the (approximately) 4 " square plate from the back of the main case to get "some" access.
you may find more than oil in there. more likely sludge, made of oil, dirt and who knows. you can make a tool from steel or aluminum that is several inches long ( flat plate - about 1/2" wide) with a 90 bend about 1/2 " long at the end. feed it through where you can and pull the sludge towards the drain holes.
I know I'll get grief for this but nothing worked for me cleaning those compartments other than ( gasp!)
gasoline .