Hmm, I’m thinking maybe we have a difference of definitions.
brine n. Water saturated with or containing large amounts of a salt, especially sodium chloride.
Salt water used for preserving and pickling foods.
tr.v. brined, brin·ing, brines
To immerse, preserve, or pickle in salt water.
You marinated your turkey in vegetable broth, but I’m not sure you “brined” it. However, I don’t know what the “cooking” definition of brining is.
In order for the soaking solution to go into the tissues of the turkey, it has to contain more salt than the fluid already in the turkey. Hence, a brine is heavily salted. The solution will flow from the area of high concentration to low, i.e., into the turkey.
That’s how brining causes a moist turkey. It overloads the turkey cells with fluid–at least the surface ones, which don’t dry out as fast and thus the interior doesn’t either.
Soaking a turkey in a solution that has LESS salt than the turkey should actually dehydrate it, causing it to be drier than it would had you not soaked it at all.
Meat that has been frozen loses moisture rapidly because the cellular integrity has been broken up by the freeze-thaw action. It becomes very dry as it roasts. It is able to take up brine faster for the same reason. Brining helps a frozen turkey appear to be juicy.
Turkeys that have never been frozen, or which have been frozen carefully, tend to remain moist longer.
The purpose to oiling the surface of the bird is to prevent moisture loss. Stuffing it can help prevent moisture loss if the stuffing itself is moist. However, if the stuffing is dry it sucks moisture out of the bird, making it even drier.