Water in the boot

[BartSimpson]

Hello everyone,
I have seen some similar posts, but my case looks slightly different. This is why I am opening a new topic.
I have a leak in my trunk. I found it out when Iooked under the boot floor cover - there was water in the spare tire bay and the left side of the floor mat was wet. I replaced the left taillight gasket.
It does not leak that much now, but the problem persists. It does not leak from the under. There is a sunroof, but I do not think it leaks through there.
It leaks only when I use a hose and spill the water on the hatch.
The hatch has 2 metal sheets welded from inside - it somehow leaks through there.
https://www.youtube.com/watch?v=yHLlXxZCwgg
Any ideas? Change the taillight seal one more time?

Thank you,
Bart