I have an 04 Forrester that has developed a leaky rear...

The water does not appear to be coming in around the hatch seal and
definately not from the floor plugs.  I had my wife spray (shower) the top
and hatch area with the sprinkler while I was inside where the spare goes
and it is coming in at the joint at the top of the well panel in several
locations, but all on the back.  It is no small amount.  If you look under
the U-bolt for the rear door latch there is a channel where the water comes
from to get inside, but I can't see how it gets there from above.

Does anyone have any idea where this could be originating?  Could there be a
plugged drain hole somewhere behind the rear bumper that is letting the
water build-up then flow over this joint?  My first thought was the door
seal, but it doesn't get wet on the inner edge.  Is it possible the roof
rails are leaking or the tail lights?

I had the car undercoated last year with Rust-Check (very thin and
drips/creaps) and I found some water when I removed the spare this year for
another spraying.  This year I used a thicker version that doesn't drip as
much but could plug a drainhole - but the water was there before the
application.

I carry a couple of kayaks around on ocasion which puts some stress and
maybe a little movement on the roof rails but the weight never exceeds 100
lbs.  Since this is something I don't check, I have no idea how long it has
been leaking, but I am almost certain it was after the first undercoating.

Help!  Winter and salty-wet roads are quickly approaching, and I have 7k km
left on my warranty...