Marketing claims that are vague, exaggerated, or unprovable are known as "puffery", such as the pizza box that says "Best pizza in town". These are generally not actionable unless they go too far. In my opinion, the claim here - "Removes up to 100% of deposits" - is pretty clear and distinct. While the "up to" caveat does provide a degree of vagueness, if they lack bona fide data to show substantial deposit removal, including some at 100%, I would expect their competition to come down heavy, probably through the NAD. I expect they know this and have some data, but still putting the "100%" in the claim is pretty daring.
One possible way to substantiate the cleaning action is to assemble a Sequence IIIH engine with dirty pistons and then measure deposit removal in subsequent runs with their oil.