Welcome to the site.  The boat is a classic design.  Anything that stays around long enough is going to need repairs.  I'm living proof.  My transomcap was made of plastic but my transom was solid when I replaced the cap.  If you let water intrude and then have 400lbs hanging off it, flexing I would imagine it would be a weak spot with any boat.  Have fun you'll enjoy owning a V20.  Here's a link to my cap redo.
 
http://www.wellcraftv20.com/gallery/album50
 
 
Again welcome!  Billy Mac