Used original 1988 Leonardo figure and customized it to look like his appearance in the original 1987 cartoon. Used Aves Apoxie Sculpt to fill in areas of the front and back of the shell, and changed the pattern on the back of the shell to match the cartoon. Sculpted a new belt directly onto the figure, in a lower position so that more of the upper body is showing above the belt line, like in the cartoon. Also changed the shape of the eyes, they originally looked kinda scared so made them a little more angry looking like the other turtles, an added the missing teeth on the empty side of his mouth. Then completely repainted the figure and Katana Blades.

Update: I have sculpted an entirely new shell/belt onto the old one using Aves apoxie sculpt, upon realizing that on the cartoon the turtles have larger shells that can actually be seen over their shoulders. Also cut off the veins on the arms/forearms and covered the toenails with Aves apoxie sculpt. Then repainted the figure. Added new pics for the update.