People say "leave it alone", again, I disagree, I had the following happen to me.
Cold morning in the arctic, plane had been outside a few days so we pulled it inside to get the snow and ice off it. Before you know it we got a wet floor and a clean plane so we put it back outside and the mechanics pull in their "project" for the day. About an hour goes by before the weather at destination improves enough to get going, with the plane sitting outside the whole time. I make my way out to the plane and (out of habit) I turn the prop a bit as I walk past, but the darn thing won't move. "Strange" I think to myself, so I get a better grip and pull slightly harder to make sure it wasn't my imagination, "very strange", I think as it won't budge a millimeter. I head into the hangar and get a mechanic to take a look at it, after about a minute of investigating he tells me that there's ice all over the area between the prop and the engine. What had happened was ice had melted gotten into every crack up there and when we wheeled it back outside, it had refrozen and it was SOLID as could be (-40 outside at the time). Took a Herman Nelson a few minutes to get all the stuff out of there but the lead mechanic mentioned that if I had tried starting the engine like that it would have (in all probability) downed the plane for a few days at least.