[Fruity]

You should be able to see traces of water stream if it came from door seals.

Anyway, remove rear rear backrest, parcel shelf and C pillar trims to trace it. I hope your car has a roof mounted area otherwise it looks like the rear screen bonding is the issue. If that is the case, it is normally due to lack of quality in factory finish. A part not adequately protected starts corrosion which swells and lets water in.

I hope it's a leak at base of radio aerial. Better than being rear screen mastic seal. If it is the seal, fix it properly and do so before screen breaks.

 

[Fruity]

I doubt it is the side glass. I didn't realise it is a SW. I should have looked more closely. Have a look at the tailgate wiring where is enters the car body. That could be a water ingress point but if the aerial mast leaks, I think that is the issue.

 

[Fruity]

OK, 1st picture looks like the draught seal at the top of the door aperture. It is not a water seal. The water seal which fits onto the spot-weld flange is already removed. I suspect the part of the headlining which is in the 1st picture is where the water then gets onto the C pillar trim (pictured earlier). If correct, that indicates a leak at the aerial mast.

I'm not sure about the 2nd picture. It look like inner sill to floor area at a seat belt anchorage. It is not clear but I guess the dark spots show moisture.

 

[Fruity]

Cleaning may have solved. I don't put anything on seals. Try if you like but I cannot advise.