Have a MX5100DT. In the process of changing the fuel filter, I rotated the petcock to the "off" position as as the arrow indicated and as I have done in the pass. Upon removing the large nut and bowl, some fuel continued to run. I immediately checked position of the petcock to make sure it was in the "off" position and it was. I proceeded to change the filter with fuel still running slightly. I rotated the petcock to the "on" position and as expected, fuel flowed more. Closed the petcock again and completed installing the new fuel filter. "Off" position is up with "on's" on both sides. I have changed this filter in the past with no fuel leaking pass the petcock valve. Also the fuel valve has two "on' positions and one "off" position. My owners manual does NOT indicate this only the "on" and "off" petcock positions. Could this fuel valve be designed with a "reserve" fuel position kind of like a motorcycle/atv? OM does not indicate this. Once the filter was replaced and nut installed everything find with tractor. I believe the petcock is just a "barrel" type valve. Also, and as expected, when I turned the fuel valve back "off" with the tractor running, engine continue to run indicating fuel was still passing through the fuel valve when "off". Tractor runs fine and doesn't miss a beat at fuel throttle. Has anybody else experienced this issue or suggest a possible problem. Tks.