hydrostatic

Trying to remove the Drive wheel using puller and mallet, it did come off but axle came off too. Axle is back on and secure but need to refill fluid. Question is how much and what type?

My troy bilt horse xp hydrostatic 46" cut riding mower will start and the engine runs fine. The blades will engage and operate correctly when engage the PTO. But it will not move forward or backwards when try to put it in gear. What do I need to do to get it to work and drive?