Glass-silicone-glass bonding (tension vs shear strength?)

[theicecreamda]

I'm attempting to repair a glass aquarium.
Here is a drawing I made when I ordered it originally,

the top brace has developed 2 small cracks.

So I'd like to empty the tank, then remove the old brace, and replace it.
But I'm trying to figure out what dimensions I need the new piece to be.

Can it be cut to match the outer dimensions of the vertical sides, and sit on top?

Or does it need to sit inside, flush with the top edge of the vertical sides?

The first style would be a lot easier to do in this situation, but as it sits, the brace is in the second spot.

Why can't I find anything about the differences between shear and tensile strength of this joint? Does it even matter? I can see that the vertical edges are experiencing both of these loads.

edit: I found this
http://www.mgchemicals.com/products/108.html
Cured Properties - MECHANICAL
Hardness 30 (Shore A)
Tensile Strength 28 kg/cm2 (400 psi)
Elongation 450%
Tear Strength 8 kg/cm (45 lb/in)
Peel Strength 7 kg/cm (40 lb/in)

 

[Navin A S]

Shear Strength 14 kg/cm2 (200 psi)It looks like the shear strength is the limiting factor in this case. So if the glass sides are strong enough to withstand the forces of shear, then the brace should be fine. Otherwise, you may need to modify the design and either reinforce the glass sides or use a thicker brace with more shear strength.