I have a Viking hydro(1996 model) that has been used only for homeowner use.I'm the 3rd owner,but it has low hours and is in great shape.My question involves the hydro filter.The manual says to change it every 500 hours/or anually.I put maybe 50 hours a season on the mower.I thought of 3 scenarios: (1)Change the filter every 3 years or so. (2)Pull the filter and drain the filter to get rid of any water condensation.Then put the same filter back on and add the necessary amount of Mobil-1.Do this anually. (3)Use a "non OEM" filter and change anually. With filters running $18-19 each and 2 qts of Mobil-1,an annual change is Over $30 and seems like overkill.Your thoughts?Thanks!!!