Small Engines (Lawn Mowers, etc.): Wheel wont turn on Walker ride-on, synthetic engine oil, power steering fluid

Question
QUESTION: Hello! This is my first post and I'm hoping someone can help me out. My husband owns a 1999 Walker Model MC ghs riding mower for his lawncare business. He's had it for a couple years and just recently, the left tire stopped turning. When you start the mower, it will turn fine but after about one minute, it stops working. We've checked the transmission lock out lever and it is in the correct position to disable 'freewheeling'. We don't want to buy a new gear axle drive assembly (part 6200-5) or even take it apart if we don't have an idea of a possible cause yet. It acts as if it loses power steering fluid when started but the fluid is full (on top of the fact that it operates just fine right when started). Any ideas would be greatly appreciated!!

ANSWER: On the transaxle there should be a sticker that has a manufacturer name and model number, can you give me those?

---------- FOLLOW-UP ----------

QUESTION: A '99 Walker, Model MC.  I think we fixed it though.  We put some Lucas rack and pinion oil in it and it seems to be working.  Thanks!

Answer
You have to be careful about what oil you put in a Hydro unit.  Some require hydraulic fluid, some engine oil in various viscosities and a few require a heavier oil.  This is why I asked about the hydro unit model number.  I believe your pump would use 15w-50 Synthetic engine oil in it.  I don't know what Lucas rack and pinion oil consists of, but a too light oil in the pump will greatly reduce the pump life.