Getting new windows so we decided to repair some moisture damaged drywall. We found the there was a gap next to the exisiting window that allowed water to get in for quite a while now. This is a bathroom on the 2nd floor. I found that the extrior sheathing is pretty well shot in some areas. Is there a way to repair the sheathing from inside the house? We have vinyl siding on the exterior of the wall in question. What other options can anyone give me ?