Wheelmanrob, I just went through weeks of trying to find my leak and found it to be the same as yours. Mine is a 2021 Escalade that I just bought! I'm confident the TSB will fix the issue but the reason the TSB was issued IMO is BS. The grommet you originally saw connects the drain line from the forward sunroof drain into the cowl, right under the glass (same on both sides). There in the cowl it meets water coming off the windshield and everything else. If you want to see it, just pop off the plastic connectors that run the length of the plastic cowl cover and peak inside. To take it all the way off you will need a gear puller to get the wipers off. But the grommet the line connects to is also the spout. Design issue here, the spout (grommet) is nearly horizontal. So when water drips out slowly, the surface tension will let the water run back toward the firewall and then down into the cowl. As it runs back, it seeps behind the grommet it just came out of. On mine, there is very sloppy body seem applied across the hole. There are three prongs that hold this grommet in with tension and in my case two couldn't press in correctly due to the thickness of the seem seal. There is a rubber seal on the inside (cabin side) of the grommet, so I guess I could have removed it, cleaned the sealer off and pushed it back tight to create a seal from the back. But it is such a tight space back there I went the lazy route and put some tubing on the end of the grommet and made extensions. I bought mine from Lowes for $8 and heated the end to make it easier to slide on. Like I said, mine was only connected with one little tab so I was carful not to push it back inside. I bet all anyone needs is a couple inches of tubing just to get the water down and away.
But yours is already gone and you have water going into the body. I can't say for sure that this is bad, but I have evidence it could be a problem. Have you removed your passenger side carpet, or peeled it back to expose the plugs underneath? There are 4 I think, they are circles of plastic pushing into some foam sealer. I ruled these out as a potential root cause early on by putting water on top and seeing if I could get any drips. I didn't, but what i did find was water from one plug area would seep between the two sheet metal panels and come out another hole. I would be concerned in your case that the water could flow between the multiple layers and end up coming up somewhere else. Also, the original spout dumps into the cowl which is wet area. You probably won't get anything pouring in since it is up so high, but it just doesn't feel right and surely there will be some weather that gets in like humidity, cold air, etc.
And for anyone else who might read this and still think they could have a leak from the A/C or evaporator outlet (like so many older GM trucks had...), you don't. I went there first and the drain is as big as my pinky without any rubber flap, nozzle or anything else that could restrict flow. I scoped it and its a straight shot just a few inches to the bottom of the evaporator. This is a redesign for our body style and is extremely hard to get to, centered in the firewall directly over the transmission bellhousing. But with this I think they got it right.
