Checked the oil on my '99 740iS today for the first time in a while and it looked very dirty and had what I could only describe as sludge on the bottom of the dipstick. This after only about 3,000 miles on the car since I bought it from a dealer where it was supposedly changed as part of the CPO warranty. I've changed my own oil for close to 30 yrs now and I've never seen that on any of my cars. I've still got 3 or 4 bars on the maintenance indicator showing but I'm planning on changing my oil every 5k from now on. It sure can't hurt. Also anybody recommend/not recommend an engine oil flush treatment?