Mazda 2 (2015) DL (sedan) - water ingress in tire well. Mystery as to where it came from

There's been a lot of rain in Sydney, Australia. I could hear swishing water when I drove and checked the boot. The tyre well was 2 inches deep in water.
The carpet backboard above the tyre was dry, so water must have entered below this.
I removed the plastic plugs, drained the water and dried it out.

Now to find the source ...

I removed all the plastic trim, and carpet. I hosed the rear of the car, went through a car wash machine and its been raining again.
Bone dry - no sign of where it got in. Its a mystery. Now I am thinking it could have entered while parked or while driving perhaps.

Any ideas as to the likely source?

I am thinking it could be:

1. Rubber boot seal (was not wet, but when I lifted it, the white sealant underneath was sticky and crumbly)
2. Rear lights (again - not sign of water)
3. There are ''air-flaps'' on the left and right behind the trim (not sure what they're called but I assume it allows air into the boot). When I pushed the flappy bit out, they black rubber felt a bit damp on the outside but no water was on the inside. (I was thinking water may have entered when driving through a puddle)

Thoughts - are there common areas of ingress to check, or should I replace the boot trim and see given the state of the sealant?

thanks

 

Certain Mazda 2's had issues with the seals on the boot lid lights.

You will need to strip out all the trim panels around the boot & tailgate, hop in the boot with a torch while someone hoses down the outside.

 

Thanks @grim_reaper . I removed all the trim and took a closer look yesterday.
I could see condensation on the side of the boot rubber itself, and the metal body work. On closer look, the boot rubber seal in this area is warped and the white sealant under it is in bad condition.

See photos: https://imgur.com/a/Gg5Q6G9

I suspect this is the place of the water ingress, but will dry it out and hose down.
Looks like this boot rubber needs to be replaced.

 

Update: the mystery continues. I took a pressure washer and sprayed the outside boot area (around the lights, rubber seal) as well as under the rear tyre arches.

Result - totally dry. Not a drop of water in the vehicle.