No lanolin, you don't want anything with oil or wax. Gore-Tex is a porous membrane and the whole premise is that it's pores are bigger than water in its vapour state but smaller than water in its liquid state, thats what makes it breathable and waterproof. Oil based products clog the pores and make Gore-Tex much less breathable. All you need is a good silicone leather spray or ones that you dob on with an applicator. Wash all of the mud and dirt off of the boot, let it dry completely and then keep applying the product until the leather won't soak any more in. Usually takes 2-4 coats. Your boots were originally treated when you got them but it wears out and you always have to keep doing it. The Gore-Tex bootie is underneath the leather and it only keeps water away from your foot and the insulation. It does nothing to the leather and leather will soak up water like crazy if untreated, and it makes you think your boot is leaking. One of the best ways to see if it is just a leather problem as opposed to a leak in the Gore Tex is to compare your feet after you take off the boots. If one foot is much wetter than the other, chances are it may be a leak, but if they are both equally damp, it is probably an issue with the breathability caused by wet leather. Hope this helps,
Patrick