I'm not sure about other brands of mowers but if you have an Exmark or Toro/Exmark ZTR you really do need to make sure you do the hydro system maintenance. My buddy brought his Exmark over and we changed the filter and drained all of the fluid from the reservoir. His mower has 239 hours on it and it was bought new this year. Just for kicks we cut the old filter open to see if there was anything inside of it. We were amazed to see a lot of crud inside of the filter. It was actually caked up on the filter media. I don't know if this is normal or not but it sure was scary looking. It was the dirtiest filter I have ever seen.