Actually a product like MMO will keep an engine spotless and if someone were to start using 10% to 25% MMO per Oil Volume on each OCI they would never have to worry about sludge.
Auto-Rx on the other hand needs oil flow and heat to combat sludge, and since arx does not work well under splash lubrication then it cannot fight the sludge.
I like to think of using MMO in the oil as preventative maintenance. MMO does just as good of a job of preventing sludge as well as it does in cleaning up the sludge.
If your engine is made out of Aluminum or if you have Aluminum Cylinder heads do not expect auto-rx to work since aluminum is porous and arx has a hard time removing these contaniments.
Auto-Rx needs heat to work and since Aluminum dissipates heat 5 times faster than cast iron then arx has a problem. The other problem is that arx was never meant to be used in automobiles since it was designed for printing presses where the internals are made out of cast iron.
Would Synlube clean up a dirty engine as well as MMO, or is Synlube meant to be used on a new engine only, maybe Capatain Kirk can weigh in on this subject since I do not know if Synlube has cleaning abilities like MMO.