What year and model do you have? The wood block is usually wrapped in glass tape and putty so you cant really tell its a wood block until you pop out the old scuppers. Here's a link to pics of my 72 Seafari scupper repair. In the 9th picture you can see a mirror image the epoxy flowing in at the base of the wrapped block, where the water was was doing the same. Block shrinks and expands with moisture over the years. Eventually brass tube separates and water starts rotting wood block, leading to the cracks in the putty, and water ingress...or something like that. Common problem, easy fix.
Good luck. Lot of threads on this. Good luck. As far as tooling goes, I knocked the old brass out with a piece of pvc pipe. Others have used sockets and dowels, etc. The flaring tool is made by moeller and available from clrmarine.com for about $35'
http://s261.beta.photobucket.com/use...upper%20Repair