To my experience emerging of water depends strongly on winddirection and most water is emerged via the groove in the back of the mast. During a shower of rain I saw (quite a lot of) water seeping out of this groove below deck.
My plan is to plug the groove with builder's foam at or just above mast transit level and apply some two component silicon rubber on top of it, as I think foam is not water resistant over the years. Also silicon rubber levels out horizontally which improves draining of collected water. I will keep you informed,

regards,

Herman Speckmann
The Netherlands
Herman Speckmann