Jim,
I don't think the soaking time is the problem. Some people, as you see, don't soak them. Some soak them in water(!) The SU DVD instructions call for about an hour. The SU instructions that come with the kits recommend overnight. You just need to make them a little pliable.
A real possibility is that the large cork washer on the aluminum collar may have been "crimped" a little. i.e. an edge may have extended out over the edge of the washer. If that is the case, a leak is possible (though not inevitable). That's where the careful use of flat screwdriver to gently push the cork into place will help.
Do check those small corks, the two concave washers that separate them from the jet spring, and the large cork and aluminum collar. It seems to me that the problem should be in that area, if the leak is, indeed, coming down through the jet.
Here's another possibility from another source: "The large rubber seals that seal the float chamber feed to the carb where it attaches to the throttle body can leak if overtightened or the little steps are folded over. Looks like a leak from the jets. Take them off and reset the seals, then tightend the bolts with gas in the bowls until the leaking has stopped."
Also... be sure your float valve needle and valve assembly are clear of debris. If it is clogged, for some reason, you can get a leak out the jet. Make sure the valve outlet is clear.
By the way, have you installed an electric fuel pump? If you have, it's possible that it is creating too much pressure and causing the leak. Just a thought...