Hey I want to let you guys know,,, ,I just changed my oil and filter again.I really checked out that little o-ring,#25....It is not smashed,nor worn,still flexable and still is perfect.I have never changed it in the numerous times I have changed my oil/filter.So,in my opinion it is not necessary???,,,,UNLESS it is damaged which I do not see how that could happen.......Happy New Yrs.......