I could use some advice for this. I’m pretty sure this seam needs to be sealed. Neither my body guy or my paint guy addressed this before getting to this stage obviously. Seems like it would have been much easier to do without the gl*** in the car. Any recommendations on what to use and how to do it now?
Looks like the space between the windshield molding and the header area. If so it is part of the windshield frame and should not need sealing. Someone probably did that to fix a leak at the windshield gasket. The windshield gasket takes care of any leaks in that area.
It is the seam between roof and windshield frame. Yes, it should have been seem sealed. They probably thought it would be covered by the windshield seal/moulding, but it isn't. The only way I know of to fix it right is to scuff, seal and repaint the area. This is going to is impossible with windshield in. I'm not saying somebody doesn't have a way to make it better, but that's the only way to do it right.
You should be able to use the same method as seam sealing a drip rail. Mask off either side, run a small bead and smooth with pinky finger. Keep a rag handy to wipe off excess on finger and pull masking tape once it starts to set up.
Just like Zax said^^^. I used this stuff when I seam sealed my floors. It's high end quality sealer at 1/4 the price of specialty automotive sealer. I used a couple of cases of it when I painted my house. Good enough for a house, good enough for a car. Also, I see your roof is painted white so it should all blend right in!