I see this tread quit often. I've had many toyota's and I believe this sludge problem goes futher than just Toyota. It's just toyota's problem seems to be worst. All my vehicle have gone over 100K and none has had any oil issues. The big problem with dino oil is sludge in the form of water. Most people do not warm up their vehicles enough to burn this water out which turns into sludge. To alleviate this problem, one can change over to a synthetic of a PAO package. This is what I use along with Group III synthetics and never had a sludge issure. Need to remember, synthetic don't mix with water and has a higher detergent package. Too many of us read the manual and do as they say about oil changes but, don't drive in the manner your instructed to. I see this same problem with automatic transmission except their problem is from heat. Dino oil starts to break down at 250 degrees and seperates and that's the discoloration you see in automatic transmission fluid.