I did the edge modification on the original CB. (Like K.C. I missed a perfect occasion for making a replacement, because I needed to put the boat back together).
I took 3M "High strength marine filler" and spread it along the trailing edge of the CB. Then I took a piece of wax paper, folded to make a long strip forming a shallow V, and used that around the filler to form it into a V shaped edge. Taped the wax paper to the CB while the filler was curing. Then sanded off the bumps and in the rear, sanded it to a 1/8 square section (actually shouldn't be quite square, one side should be a little further aft to help shed the vortices). I then faired over the transition between the board and the about 1/2 to 3/4" extension and on the leading edge, I bulked it up a bit to have a nice circular cross section. (Added some filler and fairing compound to widen the front 1/3 a bit, all in an attempt to get a bit closer to a real foil shape).
Anyway, I haven't had any hum out of that CB since, but a replacement might give still better results.