I wonder how clean and how long EGR cleansers and other techniques other than mine produces a fully clean EGR cooler. When I was cleaning mine, I was not worried about leaving a "film" inside the EGR cooler. I was more concerned about the thick and possibly "flaky" deposits left behind that might come off in service and find itself in either the EGR valve, go through the intake manifold and into the engine. With ultrasonic cleaners that apply force to the deposits, there is a possibly. Based on this case, I believe the time and work to get the EGR cooler fully and "squeaky" clean was worth it. On that account, dealers will do no less than to install a new EGR cooler. A check of eBay now compared to a few months ago reveals that price of a Gen 3 EGR cooler has risen, as the issues with the coolers' clogging has become readily apparent. Likewise, the number of listings of offers have declined. Still, as I did, the prepared owner of Gen 3 Prius models should buy one, clean it fully, and keep it stored away in anticipation of needing it at the 100k mileage. With replacement, the newly removed EGR cleaner can then be cleaned and stored. With the demand ever increasing for used ones and Gen 3 cars increase in mileage with age, the used coolers will likely be in demand for years and will not likely become useless for many years to come. Time will tell if and when Gen 4 EGR coolers may also become an issue. Finally, fully clear liquid after a one week long soak with solvent, is the only way to tell that the cooler is completely clean.