Soaking parts in WD-40, believe it or not, is actually bad for the parts unless you take the time to re-lube the parts that need lube or rust protection.
WD-40 is a solvent and only BARELY functions as a lubricant because of the fact that it DOES dry up fairly quickly. Whatever oil/grease/lube you had on the part has now been dissolved by the WD-40 and has been washed away during the soak. This means that THOSE surfaces (which may not have actually gotten wet before because there was lubricant there) are NOW open to rust if there's any moisture at all in the air. Now you're going to have to make sure they're clean and have rust protection before you put it back together.
Rain and water aren't death blows to firearms so long as you are diligent about cleaning, drying and lubing the guns. My guns are exposed to inclement weather fairly often and my cleaning process is always the same. I don't take any extra steps - just the same steps - and I don't have rusty guns.
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