Have a Ford 6640 with hydraulic brakes and clutch. Wheel cylinder blew, which is inside the rearend housing. I blocked that cylinder off since the tractor is used very limited. No racing or hi way use. Soon the other break cylinder blew. The mineral oil brake fluid was $28 a quart and had to fill the reservoir about 2 times a week when feeding hay. The mineral oil is used so as not to contaminate the hydraulic and transmission oil in case a wheel cylinder blows. The tractor requires a special additive in the hydraulic oil (134d), so I thought why wouldn't that work instead of the mineral oil. It did. It worked fine for about a week. Then the clutch pedal went to the floor. Clutch and brakes use the same reservoir. That oil ruined both master cylinders. New brake cylinders, both master cylinders, $3000 repair bill, the tractor is back at work. Expensive lesson.