Well I thought I had a clean engine (used Delvac 1 previously which is highly detergent). Wrong. 1st clean 800kms the filter (PureONE) had just so much crud in it. Did a 2nd clean about 1500kms and same. I'm now some 2,000kms into a 3rd clean, I hope to run it for 5,000kms. Tappets getting noisy already but so I'll change filter tomorrow for the remainder. Dunno where the gunk is coming from, but my guess is the piston ring area. This Mazda turbo is used as a test vehicle for many fuels/oils/additives etc so I probably wouldn't follow my methodology, but I wanted to see for myself what extended cleaning periods with Auto-Rx achieved.