I use Kiwi shoe polish. Oiling them helps if you want to take it a step further.
Good socks work well to help keep the moisture from sticking in there, but you are going to need some old-fashioned tricks to keep your feet completely dry. Most of the water, however, comes in through openings and ill-fitting joints.
The leather itself can take a mighty wet beating if it's regularly oiled or polished in a traditional manner. You really need the protection around the spots that are going to let the water in. Once it gets in, it's not coming out, no matter how fancy your boots are.
I've got a set of regular old Georgia boots that I've stomped through countless swampy areas in, with no issues. Simple combat boots have served me well in very wet and snowy conditions, as well as in service. You don't need anything fancy.
My Gore-Tex lined Eccos work very well, but the same issues apply. Water is going to get in one way or another.
Wax, polish, oil, sealant, gaiters, and good socks. That's how it works. There isn't a way around it, unless you either wear overshoes or wellies.
Cheers,
Kennith