RE: accidently put in filter oil instead of afterrun oil
WD-40 is unlikely to harm anything short term. There are many far better oils for storage beyond a week or so. Famed model engine guru the late George Aldrich recommended Rislone, but ATF, Marvel Mystery Oil and numerous others are fine. Hobby shop after run oil is fine too, but compare the price of a couple ounces with a quart of ATF etc.
Filter oil in the engine should be a non problem. Just wash it out with model fuel, Gumout carb cleaner ,MEK or any of a dozen or so other solvents and run the engine. Flood the engine? Pour the excess fuel out the exhaust or glow plug hole or simply let the thing sit awhile.
BTW, a conversation with a competent gunsmith will convince you that the only use for WD-40 should be as a aerosol solvent, not as a preservative or lubricant. I have, however used WD-40 in the gallon cans as a short term preservative or as a penetrating oil on farm equipment etc.