I have a standalone garage built into the side of the hill. On top is a rubber roof that appears to be in decent shape. However, there is a gutter around the edges that is not sealed to the roof. Obviously I need to clean off the roof and under the flashing/gutter edge. Do I need to take it all off and redo it? Or can I just clean under and seal it with something? What do I use? Roofing tar?