Definitely re-buck any rivets you see leaking. If you smack them, and the heads come off, there is the real problem. My bro in law was going to do the Gluvit route, but we re-bucked his rivets (and found & replaced a number of them) and that boat has been bone dry for a few years now for an hour of time and $5 in solid rivets.
Many boats do NOT have a sealed keel. Guys seal the area you photo'd and it doesn't change anything, just wastes sealant.
IF you can, dry your boat floor completely with a towel and put it in the water and see if you can find exactly where the water is coming in. It might not be where you think. I have found many in sneaky areas. If your boat only leaks when moving, that is a clue.
I have a thing, where I'd rather find the leak and fix, rather than slather Gluvit inside, and I've been pretty successful. Even so, sometimes you cannot access the exact leak, so epoxy fix, it is. It's nice to have options.