Looks like the two Alan's are going to be the first to hit you.
Empty the tank, you say all the braces are looking a bit weary.
Then get two pieces of glass, 50mm wide, one full length, (front) and one 100mm shorter,(for the back),
these are glued onto the top edge but down inside the tank, level with the top edge.
These will stop any bowing.
Then replace the end braces if damaged and glue them onto the top of the tank, and those first braces.leave for several days for the glue to cure before refilling.
Warning
Make sure that ALL the old silicon is removed before gluing commences.
Just reread your post to see if I'd missed anything.
One thing is concerning me is the fact that you say the "front" of the tank is bowed.
Is that for the full height??
If so, I'd definately strip the tank down completely,
and when rebuilding it.
Put a strip along the base on the bottom against the back and front pane as well as the other suggestions.
Alan
NZKA 104
Have adequate ventilation as inhalation of the fumes of the silicon is detrimental to the health.