Those are cool little mowers. I worked on an F525 once, pretty fun to drive.John Deere F510. 2.2L Mobil 1 0w40 out, same back in. Fram Toughguard filter.
21 years old and the engine/drive unit is flawless. Deck is what fails. They do have their drawbacks as it can tear up the lawn and not cut so good when turning. First thing I had to do was disable the seat and reverse switches.Those are cool little mowers. I worked on an F525 once, pretty fun to drive.