Quoted from DCFAN:
I recommend Titan competition silicone, especially for that ring that takes a beating from the slingshot.
I'll second that. The website is great - I just ordered one of the user-defined rubber kits for my WOZ (the "easy-to-install" kit) and it was shipped out the next day. It looks great installed so I am planning to order more to install in some of the more challenging spots.
The online WOZ manual is a great resource if you want to construct your own kit. (pages C76-77)