In a timely manner, repeat the previous process of laying two ~0.0625in beads of type-II(platinum cure) RTV silicone around the inside and outside edges of the center portion's topside.

It takes a very steady hand, but when you're finished the wheel centers should look like this.

Although this bead may look small, it is actually the perfect amount needed to create a good seal. Adding more silicone won't give you a better seal - it just causes a mess...trust me!