w123 300TD rear water leak

[240dddd]

When it rains my '81 300TD is getting wet around passenger side rear corner, in front of the access door for the first aid kit and rear window washer fluid. I pulled the back panel off of the rear door but it surprisingly it does not appear to be leaking inside the door itself.

It could be the rear hatch seal and door are not sealing correctly, but I've spent some time adjusting the door to make sure it is closing tight. I don't see evidence of it leaking around the seal, but that doesn't mean it isn't the problem.

There is also water pooling in the well underneath the window washer fluid container.

My question is whether any 300TD owners have any advice about tracking down rear hatch area leaks?