Yes some of the seasoning as in polymerized fat and oil will dissolve into the food. It is just oil - I find no indication it is toxic. If it was toxic should not be using it for seasoning in the first place. It is a very small quantity.
And I don't agree with the word leach here. Part or (maybe even all) of the surface coating is dissolved. Maybe even a little warnwill ware off. Leach is to exact a component from a solid such as an acid will leech some iron from a cast iron pot.