I have a murray riding lawnmower model number 42591x8b when it starts and runs for 5 minutes cutting grass, it won't go forward any more. Only in reverse. I can only find the oil fill stick. I tried looking for a transmisson stick or something of the sort to add fluid but no luck. Any help on this is greatly appreciated.

Some of these all sealed units.
Is it a hydrostat ?

I guess, its an automatic for sure as its written on the front