First: All wood will absorb moisture and lube from your patches unless they are sealed. Just because you buy a wood block from a dealer does not mean the holes are sealed, or even filed and sanded to the best diameter for you. That is left to you. Use a dowel with sand paper to polish the holes. If you have a power hand drill, or drill press, these tools make this work a snap.
If you can find a reamer the correct size for the block you are working on, use it. You really want a block made out of a good hard wood. so that the end grain is tight, and smooth. Then, coat the holes with a good stock sealer and finish. Use the reamer after you have finished sealing the holes' end grain. You don't need finish on the surface of the wood; you need it in the wood itself. If you don't have a reamer, then use wooden dowel and very fine grit sandpaper. The ball and patch should be snug, but not a tough fit.
When you put enough sealer in that end grain, the wood should no absorb any of the lube from the patches. However, you should also understand that if you are not using a " dry " lube, the air itselt will suck the moisture out of the " wet lube " you are using. If its moist to your fingers, there is either water, or an alcohol base to the lube you are using.Alcohols(Oil, both Hydrocarbon, and plant based) evaporate, and, of course, any water based lube will also evaporate in time.
Seal the end grain and all the wood on the block with several coats of stock finish. The use of a sealer under the stock finish will keep moisture from seeping from the end grain in the holes into the block itself, and then out through the wood of the block itself. Shellac is a common wood sealer, as it fills the pores of the wood, and dries hard.
If you use a loading block routinely in the woods, or at the club at woods walks, or Seneca Runs, every couple of years the block will deserve another coat of finish, both in the holes and over the entire block. The friction of your hands, and dinks and nicks to the block from use will abrade or knock off the finish. If I am going out into damp weather, whether rain or just high humidity and mist, I like to spray a household furniture wax on my loading block and wipe the wax down a couple of times the night before the event. Before going to bed, I load the block so I don't have to do that in the middle of a dark bedroom when I get up in the morning. My loading block is the only piece of gear that still sees my short starter in use. I leave the short starter either at home, or in my box of gear that goes in the car on any hunting trip with all my tools needed to take the gun apart, etc.