Put a top knot doodah on them (I'm sure they have a proper name, but I don't know what it is ), like the ones you get on fence posts only larger. I don't think PVA will help in this situation.
yaeh, they do have a name and I can't remember it either at the mo! LOL
Wood being a natural product will unfortunetly always move and crack. (The name for those cracks is a "Shake" by the way). There is very little anyone can do to stop it. Even very dense wood such as Purpleheart, LignumVitea, etc will still crack in time given the right conditions. This does not mean to say the wood is weak and will fall to bits. You can fill them, but it doesn't always stop the problem. Certainly a capping of some sort will help, as it will help prevent rain from entering the end grain, but there aint really a lot you can do....
Sorry
It's pretty simple to make a cap and that's the best solution. However, if you soak a 20% diluted Yacht Varnish into the end grain at a very dry time of year, you will go some way to impregnating the wood. Then add acouple of undiluted coats and you'll have it weather-proofed for a few years.
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