When I got home this morning I noticed that there was some antifreeze dripping from my X. I crawled under there an seen that I was dripping of the bell housing of the transmission on the the cross member but could not find where the source of the leak is. what would the likely culprit be? If it is the head gasket how hard is it for someone with limited tools and experience to change? Another question should I have to take the heads off should I go ahead and change the knock senor while I am at it?