Use the tractor forum search utility to read numerous threads covering your dilemma and the solution. Key word combos with hydrostat, hydrostatic transmission, oil, fluid, change,.......will get you a lot of hits. After draining the old oil, fill the trans with 80 ounces of 20 W 50 synthetic motor oil of your choice. Purge air per OEM instructions. You will likely be amazed. It does not matter much that you added some fresh oil, the old oil still foams and acts foolish inside the transmission. If you decide to change the oil, let it drain a long time to get the max benefit of the new oil.

Thanks, but realy? Its only two seasons old. I would have thought the oil would have held up at least that long. I was thinking along the lines of bleed port or somthing, given the power when its in 'push mode'.
If I were to drain it, any suggestions? There is a plug at the top but no other opening that I see.

Two year old tractor, but how many hours on the clock. 50 hrs per annum average nationwide. Yours could actually have an internal wear problem, but we come right back to the same conclusion....."but realy? Its only 2 years old. I would have thought the parts would have held up at least that long."
Now, have you tried purging air by the OEM guidelines in the owner's manual?
How to drain it. Remove transaxle assembly from chassis. Remove the vent hose from the transmission. Place transaxle assembly upside down over a suitable catch container. Allow to drain for a day or two. Good luck.

One of my customers has a Cub Tank with Hydro gear. I needed some simple parts and was told it was obsolete. Built in 2007.

Just last week it started dripping from the very bottom cover that holds the pump. It's sealed by a $2 O ring, which I was able to get. Imagine an O ring gasket failing after 2 years??
The leak was sudden and bad enough that it would have probably fried the trans quickly, had it not been noticed.