Nothing earth-shattering about this, just a visual of my cleaning efforts on a 2002 Passat 1.8T with 120k miles. It had Mobil1 0-40 for most of its life at 5k OCIs. I was unimpressed with the cleanliness of the valve cover and valvetrain when I had it apart to fix a gasket leak. I cleaned out the underneath part of the valve cover as much as possible and then ran 2 OCIs, first was 5-40 HDEO, Seafoam treatment towards the end of that, then the last 5k miles have been on G-Oil. Possibly the most significant action to clean out the valvetrain was fixing the PCV system which occurred early in the HDEO OCI. Left is before all of the above, right is after. Is it cleaner? Yes definitely, though a bit hard to tell because of illumination differences between the pics. And keep in mind I cleaned the underside of the cover (bottom pics) manually, that did not happen just from the oil.