Well the silicone "seals" are only on the inside of the tank. The silicone between the panes of glass serve simply to hold the tank together.
A reseal of a 220 might look intimidating if you've never done it before, but it is fact a pretty simple and easy job. You can make it look really good if you do the proper prep work which is the hardest part imo.
Cut all the old seals out with a razor blade, then clean the tank thoroughly to remove all the old silicone or grime from the seams. You might as well do the whole tank if you have to do one seam. You can use masking tape to insure a nice looking seal if you like, but if you're careful and not concerned too much about looks you may not require it. Make sure to pour in a thick, solid bead of silicone and take your time as you work, make sure there's no air bubbles. I use a latex glove and just smooth the beads over lightly with my finger, but there are various tools you can use to make the seals look perfect.
Good luck with your project!