I have found small amounts of water in the boot from time to time over 16 years of ownership. But yesterday there was a lot. Went through the list of suggestions on this thread. It looks like there were two problems.

1. The lens for the center brake light was not attached to the back. It probably was at one time, but it was barely holding on at the ends when I got to it. I have carefully re-glued the lens. The gasket seemed ok. I wiped the gasket with silicone mold release, which I have found makes flexible seals last longer and seal better. I re-assembled. There is no question that there was water entering around the lens. The inside of the lamp was dirty and discolored.

2. Water entering the around the center brake light should have exited through the rectangular drain hole at the bottom center of the boot lid. That hole was not plugged on the inside. So why was the water not draining? Careful inspection showed that the seal for the boot lid was blocking the hole. Seems like a bad design, or the seal has sagged down? I cut a small notch in the seal so that it no longer bocks the drain hole.

There is rain in the forecast. I will check after the rain to make sure I have fixed the problem.

Thanks to everyone who has contributed to this thread.

 

I have found that the chrome strip at the bottom of the rear screen has lugs that push thru the body to hold it in place, and noticed after i had taken the inner trim off the hatch, water was coming in thru two of those lugs (on right hand side) and was running down the inside of the hatch and dripping down into the right hand corner of the trunk/boot My suspicion is that the rubber seal along the chrome strip onto the glass has aged and is letting the water past the weatherstrip and it then leaks thru the plastic clips that the lugs go into.

I used some silicon sealant from underneath/inside the hatch to seal the lugs and to stop the water and this seems to have solved the problem.

As mentioned previously - best thing is take off the inner hatch trim and sit inside to watch whilst somebody else pours water from the top.