Re: Help pinpointing a leak
So you sailed 20 miles? We're you taking any water over the deck? Heeling far enough to put the rails under?
What about your icebox/cooler? Does it drain into the bilge (this one has scared me before).
Otherwise there are only so many holes in a boat hull. I'd go find them one by one (you should know them all anyway) and look at them closely. Open all seacocks (or at least the ones you had open) and watch.
It's notable that the P.O. didn't have an electric bilge pump. It's less likely he had this problem given that an it's more likely you're missing something more simple than a below waterline leak.
1979 Contessa 26