Through countless years of back and forth on this same topic WD-40 is not caustic to o-rings now, nor was it then. Kerosene is recommended in the manual because manufactures are not into individual product support and is a great way to go. Usually is more cost effective because you buy larger bulk amounts at more favourable prices.
Each person will have their own methods of what works for them; however my best method over the years has been to set the bike on a rear track stand after a good ride and set in with a good set of rubber gloves and one or two shop rags. I usually keep one that I have used for applying the WD-40 separate from the one with chain lube so as to not mix them together.
There are some pretty good brushes on the market, but the one thing you want to avoid is one that will chew away your o-ring from too much cleaning, too much pressure and abuse. For this, I recommend a horsehair, fairly stiff painting brush. They're fairly inexpensive compared to the price of a chain.
I mark the chain with a blue piece of tape on one of the links so I can tell when I have made a full rotation, turn on some music and start out. Once I have cleaned out all of the gunk, I purposely rotate EACH link pin to know that it isn't still filled with debris. Meticulous? Yes, but I would rather know I spent and extra ten minutes on it that to feel that I short sheeted the chain and potentially myself if something results in failure.
When done; saving going out and about to warm up the chain, after safely checking everything, I will place the bike in neutral ON THE REAR STAND - WITH THE REAR WHEEL LIFTED
(WARNING - IF YOU ARE NEW TO THIS AND HAVE NEVER ATTEMPTED THIS,, DO NOT DO IT!!) once the engine is started and idling, I will shift down into first gear and slowly engage the clutch and spin the tire and chain. This is an old racer track tip, so be careful and extremely cognizant of your surroundings if and when doing this!
Improper setup and/or surroundings can lead to catastrophic conditions! So, after a couple of minutes or so and after you FEEL the chain has warmed up, place in neutral again, turn off the ignition and apply your chain wax.
Once applied I will check chain clearances. You will have to take the bike off of it stand once proper tension is set and sit on the bike,,, but that is a another topic all together.
Just my two cents. Hope that helps one or two.
