Just a note on this “seafoam”, or similar products. They do work great! But, the fact is, they are nothing but plain aromatised/colourised diesel fuel. Yes, plain diesel does the same job. Prooven. Freed my tared piston rings right away. Diesel does decarbonise a engine! In fact, a periodical internal engine bath with diesel was advised in early Mercedes and Man trucks manuals. Run the engine with diesel instead of oil in the crankcase for a short period of time, drain, fill new oil in.
I think a squirt of diesel wuld do a good job in rinsing a tarry intake valve in case neaded, and wuldnt hurt the engines lubrication sistem.
Anyway, be it grease, oil or whatever, l think the valve lubrication system is genious!
Edit: forgot to mention. There is a expresion in my language that says something is a hoax, a fraud or has no value at all. It literaly translates as “sea foam” coincidence?