ok got the hub off and made a new gasket. track tensioners work well with an air grease gun. not sure about adding oil to the diff. looks like a combination of hydraulic/ diff oil sharing the same reservior and housing!!!
Be carefull when you choose to use a powered grease gun on these cylinders
we have a unit in the shop right now that belongs to US fish and wildlife that we are repairing because they overtightened the adjusters to the point they
bent the rear axles. to much track tension robs HP and causes premature wear on the sprockets, hard on the rear bearings,axles, and will cause the belts to stretch. if your belts on any machine get stretched to far then your pitch at the front sprocket is wrong and you start to have wear on your sprocket.