I just changed the oil in my recently acquired used XR600R. The oil was pretty grim. The level was fine, and the bike doesn't burn oil, but the color had a silver/grey tint to it that I didn't like. My plan is to run the new oil and filter for a ride or two and then change the oil again. When I do the next change, how important is it that I open up the engine case and clean the internal screen? I will definately clean the screen in the downtube and, of course, replace the filter, but I don't really want to deal with cracking the engine case if I can avoid it.