They can be tough to pinpoint, for sure, but some typical spots in the front are the marker lights and the windows. anything attached to or sticking out from the trailer up there could be leaking. (radio antenna? etc...).
I'd put a fresh bead of parbond on every seam in the endcaps, and the first main bow. also, the seams in the front lower panels, above the a-frame.
another common leak is at the "rub rail"...the molding that covers the joint between the banana wraps and the skins. If water gets behind that molding on some trailers, it gets dumped right onto the plywood floor. just go around the perimiter of the trailer, and gently push on the outer skins just above this molding. anywhere you can make a gap by pushing...seal it up w/ parbond.
'73 Safari 23'
'00 Dodge Ram 1500 4x4 QC