Resealing / removing silicone from the top edge

[exscape]

Hi!

I need some advice regarding the resealing of a 520 liter (138 gallon) freshwater aquarium.
All the silicone from the bottom and sides has been very thoroughly removed, and the glass cleaned with isopropyl alcohol. However, getting the top edge clean is next to impossible, at least with the tools I have (razors and a segmented blade utility knife).

All the glass panes are joined with nice 90 degree angles, which makes it (relatively...) easy to get rid of every last bit of the old silicone from the bottom and sides.
However, at the top, the glass is joined with a metallic edge around the entire top of the aquarium. The shape of the inside of this metal is such that it's impossible to simply cut the silicone away with razors and knives; it has multiple angles, perhaps 45-ish degrees each, with a flat bit in the middle.

My questions here are:

1) Do I need to silicone the top? I figure that the aquarium shouldn't be filled such that the water level can ever touch it that high up.
2) If it is indeed necessary: does the seal need to be water-tight, or is a sloppy job OK around the top, provided everything that will be underwater is done very thoroughly?
And finally, 3) If I really have to, how can I get rid of the remaining silicone? It's still several millimeters thick all around, so it's not just some scraps that remain... but it's highly damaged from the attempts to remove it.

Thanks in advance!

 

[exscape]

I grabbed a picture to hopefully make it a bit more clear: http://i.imgur.com/3msuSlC.jpg
(It truly looks awful in this amount of detail!)

You can see the odd-shaped indentation as it's filled with that lovely brownish color.
It looks to me as if it's far enough away from the glass that it shouldn't cause much of a problem with bonding/curing though; would you agree?
More cleanup is obviously needed in the corner, and probably along the edge to be joined as well.

 

[Delapool]

I'm just trying to picture this - is the photo of the inside of the tank? Unfortunately can't help much so hopefully someone knows.

 

[exscape]

I'm just trying to picture this - is the photo of the inside of the tank? Unfortunately can't help much so hopefully someone knows.

Yes, indeed. The photo shows one of the top corners, from the inside.
I attempted to annotate the picture a bit, not sure if it helps at all:
http://i.imgur.com/OWz9PKc.jpg

I believe that cleaning the glass and the part of the metal "before" the indentation (the part highlighted to the right in the picture) should be enough, but I'm not certain.
Even getting that part clean might be a huge pain, though; I've tried, and didn't get very far.