I think that the problem of the evil sludge is over rated in our MODERN motorcycles. First In many cases it is a combination of not changing oil at proper intervals and a cool running engine without positive crankcase ventilation (PCV). Old non detergent oils are also a friend of sludge. The cool running engine without PCV tends to accumulate water in the crankcase which is also a sludge helper.

We all use modern proper specification oil & filters changed at the recommended intervals, don't we? motorcycle engines tend to run towards the hot particularly on newer ones which with their emission control systems which ventilate the crankcase and discourage moisture development.

Some feel (as I do) that in most cases the minimal amount of material (sludge, metal powder etc from wear) that collects in the sump of MODERN engines will stay there and not be a problem at all. Some also believe that running a solvent in a clean running engine potentially will stir up the crud and send it through the oil system. If you are that worried drop the oil pan & check.

I heard of a fellow who would use a what he called a "waste" quart of new oil. After draining out the old oil he would replace the pan plug, pour in the oil wait a bit & then drain and discard it. A bit anal I think.

Lastly starting up the machine & not running it up to normal operating temperature will also cause excessive moisture contamination of the oil (cold engine again) When the bike is asleep for the winter do not run it for a few minutes from time to time for any reason.