Acid flush questions

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I'm looking to do the acid flush on my engine this Spring, or during the winter if temperatures remain mild enough.

I've found the procedure here: acid flush procedure

#1. This procedure has 3 parts, running the engine, a pressure flush, and a manifold flush. Are you meant to do all 3 parts, or is the pressure and manifold flush meant to be done if you can't or don't want to run the engine? It seems to me, that drawing the acid solution in, by running the engine would negate the need for a pressure and manifold flush. Am I wrong?

#2. Does this damage the rubber impeller? Should I replace the impeller afterwards?

#3. My engine isn't very gunked up and runs at the perfect temperature, but I have observed a little black funk in the engine. I just want to keep things well maintained. Any opinions on whether an extended white vinegar soaking would be adequate vs. acid? How many folks here have done the vinegar flush?