Water that gets into the mast from the various halyard exits and such should drain off of the depression at back of the mast step casting. If it is just seeping out, it is likely that there is debris in there which you might be able to clear with a hooked shape piece of thin shim stock. See the picture at:
https://j30.us/ubbthreads/ubbthread...rch/true/re-mast-drainage.html#Post17224

GL,

-Chris