I completed the Rydlyme flush last weekend. It went pretty well -- from the bubbles and foam, I could tell that it was dissolving quite a bit of crud.
I did have one unanticipated problem though. There is a drain valve on my cylinder head, with a length of hose running into the bilge. The valve has apparently been plugged, since I could never get anything to come out. So I just left it in the "closed" postion (handle at right angles to flow).
But it turns out that that is actually the "open" position, which I discovered when the Rydlyme dissolved the crud that was blocking the valve (about an hour into the flush), and my entire supply of Rydlyme was almost immediately pumped into the bilge.
I thought about trying to reclaim it so that I could finish the flush, but I didn't have a way to effectively filter the bilge detritus, so I just pumped the entire mess overboard (with lots of water and sodium bicarbonate).
At that point, I needed to figure out how to get my hands on more Rydlyme to complete the flush, but I didn't want to wait a week for shipping like I did for the first gallon. On a whim, I stopped by the local outboard repair shop, and not only did they have Rydlyme, but their price was half what I paid to have some shipped to me.
Two lessons learned.