just to underline what's already been said, think it was wise to change the engine oil @ a few 50 hr intervals like you did on a new engine. and, as mentioned, just get an analysis on subsequent changes to estab. your change interval baseline if you are interested in it's condition ....personally, just by looking how "crystal clear" it looks to me would not be enough, too many other variables. good luck, sounds like you're on top of the maintenance schedule...are you using synthetic diesel rated oil?