Just want to chime in on a couple things...
First off, I am very affiliated with JK, but not a paid employee, just a person who helps out a lot.
There is no way possible for that or any JK to leak. They are 100% no holes to the hull. As a matter of fact JK's are a great way to see if your drytop is still "Dry" for that exact reason.
Thigh braces are VERY sturdy on rockers. The design of the boat puts your thighs very deep into the side of the boat. I wasn't there when you demo'd one, but with the 50+ days I have in both proto's as well as the production boats now, I have never had a sense of them being anything but just right.
I have never... not even once had the foot brace system move. I am curious if what you are commenting on is the 1st second you press your feet on the foot system after adjustment. It does slide an 1/4 inch from when you lock it down. That is simply the rope being grabbed by the teeth of the cleat.
But honestly, I have never had even the ever so slightest slippage. Since the first time I adjusted it I have never messed with it again.
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body. But rather...To skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming... WOW !!!! What a ride!!!!!!"