Yaaaargh - leaking again from driver handle
 

I am getting sick of this.

I am 80% certain that it is coming from the driver side corner marker light. I even put a big glop of weatherproof silicone on/over/around the grommet under the light.

Is there an easy (or some what easy) way of pulling back the head liner to see where this is coming from?

I dont sure it is from the marker if u already put silicone on it. try check ur windshield silicone.

is there a good method to do this to confirm where it is coming from?

Check your sunroof drains. Open sunroof and pour water in the front channel. Water should drain out from both front corners of channel and should see water exit out at rear of front fender area. If water is pooling and wont drain then you need to clear drain tubes out

I'll check that..I did clean those out a year ago
*I hope it is clogged - I would be beyond happy

INFO TIDBIT:
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I get a big cup of water (like 32 oz) and bring a dust pan.
I put dustpan into reservoir then dump water into dustpan which drains into reservoir.

I had the same issue. At the junction where the A pillar meets the roof, my weatherstrip was allowing water in. The water dripped from the handle and continued down the A pillar flooding the drivers floor.

Resolved by applying silicone on the weatherstrip from roof all the way down the A pillar. Alternatively, you could replace that weatherstrip, but it is $100.

Here is leak in action

Wow, that seems to be a heavy leak right there. I had a similar thing happen to me. I siliconed all corner lights and everything was fine until my front windshield had to be replaced due to a crack in the middle. After they replaced it I had a leak similar to yours. I took it back to the shop and they re-glued the windshield and mentioned that the glue chipped off in one area which was causing the leak. I didn't have any trouble since then.

Could be that the rubber seal on your windshield degraded after some time and it's letting water in ? Just a wild guess.

Try this. Start truck and put blower motor on high speed. Close all windows and doors. Get a spray bottle with soapy water in it and spray it around windshield and any suspect areas from the outside and watch for bubbles. With blower motor on high it will pressurize cabin and soap solution should locate your leak point.

Now THAT is a great idea. I will try that. If I see bubbles - I will video it before I do anything.
However - I did just put a bunch of silicone in that little groove (front of truck under corner light) this afternoon.