In reply to Matt Bill Platypus: Most good quality leather boots, tend to reply on goretex liners, lower quality leather boots, tend to reply on spray on waterproofing, or cheaper membranes, very few tend to just be leather, scarpa tend to have a few, but meindl, brasher, mammut , scarpa (some of their range) all tend to reply on liners, if your boots, your liner has failed.
Boots that are just leather how ever are not waterproof, or as such not meant to be as per manufacturer, a pair or approach shoes i got of scarpa come with a manual thingy which basically says boots the are solely leather, cannot be classed as waterproof as they dont have a liner.
If their leather with no liner, and still leaking like mad, there is nothing you can do, either leather is wrecked, and cracked through, or stiching is very poor/failed and letting water through, treating is just extending how long it takes to do this!
What boots are they?