as far as I am aware, no FULL (not a "para" or "combined with petroleum") synthetic oil will generate sludge of any type. some oil vendors are now offering "para synthetic" type oils that combine synthetic with dyno oil. sorta like mixing oil with water, why would you want to try and "combine" the two? as to your issue, the sludge might be left over from a prior "dyno" oil change or, as you say, someone slipped some petro oil into the mix when you weren't looking. In an attempt to clear the sludge, some people resort to engine flushing machines. IMHO, this isn't the way to go......a slow and gradual change to synthetic normally clears up the sludge over 2 - 4 oil changes. change early and change often.......also a really GOOD bypass filter (www.oilguard.com) doesn't hurt a thing.......

just for the record, ALL jet aircraft use synthetic oil. this is due to higher operating temperatures and maintenance issues. A mechanic for the U.S. Army once explained to me that the Army NEVER changes the synthetic oil on $750,000 jet turbine engines on the Apache helicopter. his statement gives new meaning to the term "long drain intervals".