If the water is coming down the shaft as you describe then I would assume that the o-rings on the rotation shaft are dried out or worn out and need replacing. the antenna should be lubed twice per year with dry silicone spray only (never WD-40) to keep thing moving smoothly and preventing this kind of an issue.
You can buy a whole new shaft or replace the o-rings. Once you disconnect the handle inside and remove the parts which come loose, you can go on the roof and unscrew the black cap on top. The shaft will unscrew right out for you to repair or replace.