I've got something very similar with the saloon boot lid. I cannot see how so much water is getting in the boot lid - loads seem to drain out of the lock area and the sprung bumpstops as it starts to open, and then as the lid opens further, the openings around the lights. I've removed the inner liner trim as I initially thought that was catching the lip seal and collecting water and directing it inside the boot lid - but it still does it.
Having sealed the lights and the badge, I cannot see how so much water gets into it, with the car parked. It's almost as though the nice big drain holes allow water in! Certainly don't seem to drain it.
Well, after my last post, I taped up the drain holes, just in-case local water somehow ran up hill. I proved it doesn't, as water still got in, but less drained out - so when I opened the lid, even more drained out the openings in the inner skin and lock cover (I've removed the inner liner/trim panel).
Closer look today in daylight show water running out of the lid by the hinges - so I removed the bolts holding the hinge to the boot lid - and revealed the threaded holes for the bolts and two large holes, hidden under the hinge plate. So sealed them and replaced the hinges bolts.
I removed the small rubber bung below the hinges (below with the lid open) and blew compressed air into the boot lid - water ran out the lower two corners - the leading corner when it's shut. Really close inspection revealed a lack of sealant - I can't tell if is missing to allow it to drain when open, or it's worn off. The rubber lip/seal running under the rear window rubs on it - it could of worn the sealant away. The lip does seem to direct all water from the screen down past these sealant-less bits of the lid.
So I've cut the lip back a bit, and applied sealant to the boot lid. I also replaced the small rubber bungs, sealing them with hylomar to allow me to get them back out if needed. I did the the same with the cabl grommet, just in-case.
And of course, after a week of rain, it's now stopped, so I don't know if it's worked yet.
It'll definitely rain tomorrow - I'm shifting a one tonne Cochester lather balanced on my car trailer behind the Alfa tomorrow.