Water leak from Passenger Visor Mount

[MIPS]

We had a pretty dry year and didn't really notice until about a week ago that after a rainfall I had a good drip coming down from the plastic trim joint closest to the passenger side visor mount. The headliner had to come down anyways to be resurfaced and I was able to find the area had surface rust, signs of dried water streams and when you sprayed water on the roof, a drip.



A mirror and paper strips finds it's dry above the drip and below. I inspected the seals and bushings for the roof rack and they were tight but I siliconed the screws back in when I reattached it. I sprayed water over it to verify it was not the source. I also sprayed water over the top of the windshield and it's not from there either. With the headliner removed I can also confirm it's not the chrome trim strips running the length of the roof either.
I only started to get water inside when it ran into the drain channel over the doors for a few seconds, but I cannot find any indications that it's rusted through somewhere. How was this portion of the body welded together and was it sealed? Both my lights, mirrors and cameras can't get into the tight space from the inside of the body to verify but I have no idea how the heck it's getting fromt here to where it's dripping, considering there is no signs of water running down the A-pillar.

[MIPS]

It was in the rain channel. I ended up having to take the chrome trim off and then forcing UV and heat resistant clear silicone into the channel and then reshaping it with a popsicle stick before the leak would stop.