WD-40 is seldom a good thing.

It is sold as the fix-it-all oil, but really, all it does is attract dirt and moisture .....

Best thing to do:
Fill an ice-cream tub half full with your regular brand of glow fuel. Get a tooth-brush( not the one you regularly use...)

Dump the engine into the fuel. Use the toothebrush to scrub the outside.

Remove the glow plug.

Crank the engine under the fuel a few times.

Leave it for 1/2 hour.

take it out, let the fuel evapourate.

Put the engine in a zip-lock bacg until used again.

gus