from my understanding the 5.9 has air leak issues from the factory.
seal it or use green slime where all seals are.
i'm not quite sure why anyone would use WD-40 in their nitro engine.
WD-40 really has no lubricating qualities to speak of, it is a super thin penetrating fluid for dispersing water and eating rusty nuts and bolts.
keep it out of your nitro engine.
if you're using it for an after run, it's a giant mistake, use an after run oil that is meant for after run use.
also WD-40 has the tendency to gum up ,much like castor oil.
it also dries out leaving you with a dry start on your next run.
if you don't want to spend the 4.00$ on the tiny bottle of after run oil, seek out a hardware store and locate some marvel mystery oil as it is the same as after run oil.
about 4-6 drops down the carb opening and turn it over for a count of 4 seconds(if using roto start) or about 4-6 pulls(if using a pull start)
repeat this step twice.