I had a 55 and 90 that did the same thing. I never could get the 90 to hold well enough that I was comfortable. It always seemed to work it's way apart. The 55 did fine, but I used JBWeld top and bottom on the plastic brace to hold it together, and then used a glass panel and silicone like you did. I don't know if the JBWeld made any difference, but I JBWeld everything. If nothing else it gives me peace of mind.Yeah thats to prevent bowing.
My 55g I got has a snapped brace, and terrifying finding out when I first filled it, it bowed and was a major break-risk.
I used a glass panel and aquarium silicone to reinforce the centerbrace.
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I probably could have done a neater job, but it was a heck of a nightmare as I had transferred the fish and everything to it before realizing it so had to keep it only 1/4 way full for a few days to let the sealant cure fully and securely.
But it works.
I will say with your centerbrace, as long as it is not snapped and the tank doesn't bow when it's full, it's doing its job.
It's a matter of force being pulled against the brace where it needs to hold.
A 40b has a more sturdy shape than a longer 55g, less force against the glass in a shorter more compact tank, than a long and narrow and taller tank would have.Sitting here trying to work out why a 40B has no center brace, but a 65 does. And they both use exactly the same kid.
Gonna have to call shenanigans on it doing anything except preventing bowing.