Ok, so my curiosity got to me and I just climbed back up to take another closer look. There is no need to drill the base casting. It already has a pretty good size slot or depression in it that should drain water pretty well, unless some crap has gotten in there and plugged it up. If it were plugged I would think a small piece of wire worked around underneath the mast and between the base casting would clear it up and resolve drainage issues. It might be possible to enlarge this opening by drilling or milling a matching slot in the mast someday when there was nothing else to do. My base casting also has the slots in it and the base has been pushed to the limits to the rear, which seems the opposite of what I was expecting from the Conundrum thread.
I just tried all 4 of the screws with a large Phillips head and a substantial effort and they didn't budge. So they are all now soaking in WD-40 and my next attempt on them will be with a hammered impact driver.
I do think that my idea of making a dam at the front side of the mast is still a good one. It could be done with a block like I mentioned or simply running some silicone across this front area and then along the teak. If the bead were 1/8" high it would do the trick and force the water to find that rear drain hole that is already about 1/2"
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