Hiya,
In the uk, the eg: centre top glass brace is siliconed (that's it nowt else) usually clear silicone even if tank is stuck with black
As for the scratches, i feel your pain, i grabbed the wrong cleaning pad (had been used before and was embedded with sand grrrrrrr) and off i went happily cleaning the front of my 6x2x2
To my horror i lost count after 250 scratches

actually though only two stick out if i look for them
As for removing them, this is what i've read ...........
Cerium Oxide, a polish powder from jewelers and the bay (scratch kits with mop pads etc)
Anyways ... you dampen the surface and get to work with the paste, from what i've read though if you can scrape your nail over the scratch and you feel the scratch well you might as well not bother attempting to remove it
I now see my newest tank as 'faulty' hehe What i'm gonna do is get some opti-white cut for the front and redo front and all the tanks siliconing
Also as things stand, next year i can have a larger 9ft tank either built in the room or shipped flat-pack for a friend to build up
Ohh a way to minimise the scratches from view ... i found a smear of clear silicone grease buffed into a deep scratch, but saying that by just really keeping the inner valley of the scratch really clean lessons its visual impact somewhat
(everyday i could kick myself for not grabbing the correct new cleaning pad, darn sure my next tank won't get scratched lol)
Hope that helps a bit
Tony