If Montero and/or Iuliano are wearing first team shirts on a consistent basis, this team is in a world of trouble.
Problem is, there's no one else to replace them. If tudor wasn't so injury-prone, then you may have an option. But after that, you have Ferrara, who only looks like a shell of the player he was last year, or you move thuram to CB, but then weaken yourself considerably on the Right.
Whether or not it is in Juve's "tradition" to not buy any players during January is not the issue. The issue is that this defense hasn't looked this shaky in years, and somethin needed to be done, if only to scare the current players and to get them to wake up and get in gear.
However, mental toughness only gets you so far if you don't have the talent.