[SteveAus]

Just came across an article relating to removing engine sludge, but noticed the benefits of regularly changing the oil in your engine annually and with a quality synthetic oil.
Annual oil changes are something I have always believed in with all of my cars, but I did not realise how good they are until I saw these photos.
I was not concerned about the sludge in the Kia engine (and I assume the car has been neglected for many years), but I was impressed with the lack of sludge in the BMW Valve Train (third and last photo) and how clean the mechanicals are. The BMW valve train has been photographed 10 years after using a synthetic ester-based cleaner (AutoRx or something similar), and 10 years of synthetic oil, changed once a year.

It may cost a few more dollars per year, but I will continue with my regime of annual oil changes.