If you get it tore off post the problem spots and folks with experience can chime in to guide you. Alot of times a leak can develop on the roof from the roof/front cap seam. Also check around the side windows and trim. You definitely need to find the source before sealing it up. Underneath the sheathing is some insulation and frame structure. Nothing to be worried about there.
Wish I had better pics but this project started in Feb-March and was cold so I was in a rush to button it up. It did come out good thankfully.