Small Engines (Lawn Mowers, etc.): Lwan Boy Hydro transmission, rear wheels, pums

Question
I just bought a used but very well cared for lawn boy LT 13H riding mower. The person I bought it from advised that after about 20 minutes of mowing the mower would stop moving. He showed me a schematic of the transmissiion and he said he thought it was the pums that were going / gone. I have ridden it till it did as he said, the mower would slow down then you could see the rear wheels chatter as is came to a stop. Do you agree with his assesment? Can I purchse the pumps myself or is this a "dealer" only part? Thanks for your assistance.

Answer
Robert
Have you checked the fluid in the pump? Sounds like you have a lot of air in there and it needs to be purged out and install a new filter.I really don't think it is the pump. Sometimes they just need purged and new oil.
If you need any parts for this let me know the model # and any other #'s on the mower.
Thanks