Aside of hurting the bearings there's another issue in letting fans rotate by an external airflow: They turn into wind turbines, pushing electricity the wrong way. That's way more dangerous to your electrical components than some moisture. Heck, what is the first thing to do if you drop your cell phone into the sea? Flush it with tap water! Moisture isn't dangerous if it A) doesn't contain corrosive or conductive elements such as salt or other minerals and B) if you dry it soon enough. Water is somewhat of a solvent, too, if let to sit for weeks.
Skuzzy, I've been thinking about the air compressor can from Amazon which was talked about some years ago. Did you ever get one and if you did, was it worth anything?