The advice given by the previous guy was dubious enough to make me register for an account... Yes, it will work but it will also waste your bandwidth...
I'd suggest choosing Properties, then going to the Local Files tab, and clicking "Verify integrity of Game Cache...". This will download only the files that are corrupt and you shouldn't have to worry about moving the save file.
On second thought, I'd make a backup copy of the save file anyway just in case.