Water from passenger sunvisor clip

The car is a 2012 Plugin, no sunroof. It's gone some 41000 km (25500 mi).
It's winter time (between -5'C and -15'C (23'F - 5'F) every day) and I'm wondering if any of you other people have had this issue:
There is sometimes water dripping from the passenger side sunvisor holder/clip/thingy. Not the outer joint, but the little U-shaped receptacle that the visor snaps into, closest to the rear view mirror. Could this be condensation, and is this an issue that could lead to bigger problems if it hasn't been checked? Car ran out its warranty in November 2017, so I guess Toyota aren't gonna "goodwill it" for me either.

I use a block- and cabin-heater during the mornings. It's a simple system that takes house-power from an outdoor outlet and sends it to both a block-heater (some 6-700 W) and a cabin heater (1900W) mounted on the inner passenger side footwell wall. It's all on a timer and runs from about 6 AM to 8 AM every morning, leaving the car at cosy room temperature for me to drive. The block is probably at around 40-50'C when I start driving.

I'm guessing that what happens is that the hot air condensates as it meets the cold roof panels behind the headliner and somehow converges to the mounting point of this visor? What can I do to prevent this?

 

It's cold as balls. There's no "not heating it".
Also, I mean obviously, things would be frozen and not dripping if I didn't heat it up.
I haven't used the rear washer in ages. I also think it would smell terribly if I had washer fluid for the rear window piling up in there.

 

Called my local dealer.
The guy thinks there's built up moisture in the air from bringing snow in, evaporating it, and the vapor penetrating the headliner before condensing and freezing in contact with the roof panels. When the car is stationary and getting heated thoroughly by the slightly upwards-facing cabin heater for a few hours, that frozen water up there will melt. He doesn't think it's gonna be an issue apart from when it's very very cold (which it has been), but asked me to take a video of it and see if they can't make a goodwill-case with Toyota (since the warranty IS expired).

 

It's parked outside without cover and I also have no issues with the plastic in my car.


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