I have seen some positive posts about people running a 25% mixture of WMO and not reporting any problems despite some fairly high hours logged. It seems to me I read that the Air Force was doing this same thing successfully at about 10% to 15%. So I wonder if the key issue is really the build up and concentration in the combustion chamber & piston of waste products that can be either cleared or avoided by a different fuel mixture. If that is the case (as I suspect it is), then the HHO mixture could also change that dynamic for the better. Not that it would be doing anything with the carbon and ash rather than preventing its build-up inside the engine in the first place.
Just some musings here, I burn all my waste oils in the shop heaters.
dieselgman