As a first step with any new-to-me vehicle, I drain the oil, flush the system with some cheap oil, or a flush agent, and then put some trusted stuff in the crankcase or oil tank. I am a longtime believer in Castrol products, but Honda's own stuff is good as well in the old bikes. In this case, the oil was filthy, and the filter was long past filtering. Even the housing fins were caked with grime. Somehow once you are finished with this fluid replacement process, the bike sounds better and runs smoother. If that is all in my head, then so be it. However, some things are decidedly more factual. In air/oil-cooled engines, having dirty oil has a double whammo effect: it does not cool as well, and it does not lubricate as well. Not good. There, I feel so much better now.