Meat – Is MSG able to penetrate meat like chicken breast and steak when dissolved in a brine

I'm not sure the butter penetrates, but it tastes pretty good on the surface. ;)

I think it's pretty obvious that marbling plays a huge role in juiciness, so it stands to reason that if you bard or lard the meat it would also make a difference in juiciness (and indeed, the standard filet mignon with the bacon barding would seem to bear this out).

In the end though, it's always been my experience that once you cook the juice out of something, it's gone for good. I've always considered the idea of "resting" meat to be more about letting it cool to the point where the temperature isn't going to force out juice that would otherwise linger.

Just in case, is it just something that dripped into the oven? Unless you've baked something else since you started having problems with the chicken, just preheat it and see if there's any smoke. (Or inspect the bottom, but you might miss something.) If there's any smoke heating an empty oven, then you need to clean it.

Assuming that's not it, most likely it's still the olive oil. Depending on the oil, some of it will indeed smoke at 350F, and on top of that, it's possible that your oven is actually hotter than it thinks. Unless you've checked the temperature with a thermometer, it's quite possible the temperature is 25-50 degrees higher than it claims, especially if it's old. You could try lowering the temperature further.

But really, there's not really much point cooking this with extra virgin olive oil. It loses its flavor when you heat it to those temperatures, even if it doesn't smoke. You'd be better off just using a neutral oil (vegetable oil or whatever you prefer), and if you want olive oil flavor, add a bit after you're done baking. You probably don't actually need very much oil when baking, so you could reduce the oil there, and make up for it with olive oil at the end.