Cracks in rain gutters on roof

So I've had some problems With water leaking in the back of the cab and I've narrowed it down to the rain gutters and I'm just curious on how to go about fixing it myself. I thought it would have been covered under warranty since it's a seam that's leaking but the dealer here is horrible. They want 500 just to pull the headliner to see if it's for sure leaking there and then are saying they won't cover any of it since there's not an actual seal there. Any ideas on how to seal it myself? It could be the rivets leaking but there's a pretty good sized crack there.