Wow I havent heard of any of this before.
Can anyone tell me what the final decision was as to the cause of the "sludge" in those engines?? I've never seen an engine with sludge unless the owner was improperly maintaining it, or was using cheap, crappy oil like Pennzoil (a liquid candle really).
I'm an air cooled engine mechanic and see the different effects of various maintenance practices every day in these type engines, and it's amazing how different two identical engines can look when torn down and you ask the owner, what brand oils they used, and honestly how often was it changed. There is always a definite pattern that emerges the longer you work as a mechanic and see this for a living.
I know ALL manufacturers have their faults here and there, but I dont see how sludge in an engine can be anything short of poor maintenance or using sub-standard lubricants/filtration. Slap on a Pennzoil or Fram oil filter, fill it up with some Quaker state or Pennzoil lubricant, and yeah, you're asking for trouble! Unless there was a direct culprit in the engineering of the filtration or bypass check valve in the engine that cause it to constantly bypass the filter, but that's the only reason for dirty oil, other than the aforementioned reasons I listed. Not the engine's fault.
I dont use those oils in my LAWNMOWER, much less my 25K or more vehicle!!! I use exclusively Mobil-1 oil and filter in all my 4 cycle gasoline engines. I also keep Exxon Superflo conventional oil around for friends/family/neighbor's equipment, as from real world results from where I work as a mechanic, this oil seems to be one of the better dino oils.