Is it possible to make a choice lean juicy?

Try the foil boat method and your flat won't be dry.

Meat Church just released a video on this. Some interesting stuff in there.

How would we know? You’ve told us nothing about how you cook.

What cooker do you use? There are so many variables that can be a factor here that it's very hard to tell you what can help. That being said, the biggest thing that I have encountered that leads to a dry flat is temperature variance between the flat and the point. You don't want the flat to be too far ahead of the point, and strangely enough you don't want it to be too far behind the point either. In an offset you can accomplish this in a few ways.

1) any sort of mods or hacks you can do to make temps as even as possible across the entire cook chamber. (YouTube is your friend here)

2) start with the point towards the fire, fat cap up for the first 2 hours, after that, start rotating the brisket every hour or so, but always keep the fat cap up. Steve Gow (smoke trails BBQ) has a great video on this on YouTube. Check him out.

3) lastly, spritz your crunchy looking spots and block them with foil if you can. Dab any pooling during the stall with a paper towel to avoid bald spots.

4) lastly, if you can long hold it in your oven do so. Pull the brisket early, at like 190-195ish. You want there to be some resistance but not too much. You definitely don't want that room temp butter feel. Add beef tallow to butcher paper and wrap it tight. Then wrap it again in foil. Then put it in your oven at 150 ( if your oven can go that low on warming. If not you may need to recalibrate it) for at least 15 hours and up to 20 hours. Check on it to make sure your oven does not turn off. I learned this the hard way, as my oven while it can get down to 150, shuts itself off after 12 hours. It will continue to render the fat and collagen in the wrap at that temp, and should come out perfectly tender and juicy without being over cooked.

Yes it is!

When I rest the oven at 175F, I place a large pan with water at the base. I add a cup or 2 of water to the pan the brisket is resting on. Brisket is wrapped in butcher paper. You can always leave a little extra fat on the flat, but make sure it renders well. I low smoke for first 3 hrs at 190F-225F, then raise the temp to 250F at the 5th hr. At the 8th hr it's raised to 275F-300F. There's a water pan in the smoker as well. It's wrapped in butcher and tallow added when I get a bark(~170F internal). I pull it out at 190-198F and rest it in the oven at 175F. Brisket is allowed to cool off and opened for ~20min, then placed in a pan with a cup or two of water of consome. Brisket sits on top rack and pan of water sits below. I turn it off and let it ride downhill until it's at 150F. .

Sure it's not underdone? Underdone can be dry as well, I can usually tell which causes it by whether or not it's falling apart. Falling apart-overdone, dry and won't pull apart easily- underdone. I usually buy choice, often find choice which have better marbling than prime. Fat doesn't make it juicy anyways collagen breakdown does, fat makes it yummy. Also, if you're at higher altitudes, 203 internal can be too high, water boils at 203 where I live. I'd also recommend unwrapping when you take it off the grill to minimize carryover in case you're on the cusp of overcooking. I usually vent mine till it drops 2 or 3 degrees, then close it back up for the rest period

Things that will help -

1) Buy best marbled choice you can find. It's even better if it's left handed.

2) wet age the brisket 2-3 weeks, if your can. This helps it start to get tender. When you smoke it, it will be done at a lower temp

3) separate the point from the flat before you smoke. Start the flat about an hour before the point.
You can go full Texas crutch on the flat, or turn the flat into pastrami

Inject with tallow