Hi I have a new Gravely ZT XL 48 Has the zt2800 transaxles. I have 3 hrs on it and noticed the left reservoir tank is a little lower than the cold full line. The manual discusses how to purge when you do a change but doesn't discuss if purging is needed for adding a little. So my questions: 1) do I need to add any if it is a little below the line? 2) if I add a little must I purge? 3) should this be low? I don't recall checking it cold but dd remember it was well above the line last week. Thanks!!!