I don't know if it would help valve guides or not but I have switched to Chevron Delo 400 15W-40 oil in my 261 stovebolt and noticed it has really cleaned out the sludge under the valve cover. It has also quieted down the rockers a lot and I have noticed less draft tube funk. I probably wouldn't run it without a filter because it could knock loose some sludge but I am really happy with it and the full flow filter. It only costs about 10-15 cents more a quart than Valvoline. It's certified for both gas and diesel engines.
