As mentioned in another thread, I'm adding a swim ladder to the transom this year. In my research, I've come across the phenomenon of sealing transom through holes, which up until this point I wasn't aware of (I thought the washers/bolt heads sealed them, I guess.) So I'd like to properly seal stuff, including both my upcoming ladder installation, as well as the existing througholes, or at least the lower set of 4 bolts that hold the attachment point for the rudder to mount onto, just above the drainholes.
So far from what I've read, it's good to countersink your hole, at least for the screw/bolt head, so that you can get a thicker bead of butyl tape/3m 4200 sealant in there. But for all of the holes in question for me, the outer part doesn't come into contact with the bolt head, since there's a piece of SS hardware in between the bolt head in the transom. For example, my ladder bracket will be sandwiched between bolt head and transom. And for my rudder attachment point, that part (whatever you want to call it, it has a little loophole that is the female piece for the rudder's male "hook" -- that is sandwiched between 4 bolts through the transom. So do I squeeze butyl tape behind this SS hardware? Do I still countersink the holes and try to stuff them before attaching the hardware? I don't get it.