slight peeling of 2nd hand tank..

Nope. To do it properly you'll need to remove the entire seal, and then re-silicone the area. You can get products at hardware or home improvement stores that remove all traces of silicone - I'm not sure if they're safe or if the best thing to do is to remove as much as possible with a razor blade. Basically what you want to do is create a completely clean surface and start from scratch - silicone doesn't stick to itself, so you can't 'patch' a seal.

Don't worry, it's not a difficult as you think, it just takes a little planning and time. Make sure that you use GE Silicon II from Home Depot, it's the same silicone that All-Glass uses to seal their tanks. Also ensure that you let the silicone sit and "cure" for 9 days after application.

Like I said, it's not too hard, I've had to repair a 240G, 1/2" thick glass tank before, and it's still going strong after two years.

I just wanted to suggest that if you're going to recaulk the tank, you might want to think about doing the entire thing - I was thinking, if one seal is weakening, chances are the others may be as well, even if you can't see it yet.
If the GE Silicon II is available in black (and if it's safe, of course) I highly recommend using black - my new 65g came with black seals and it's SO much nicer than clear. With black top and bottom edges, lights, stand and painted background, it fits in and you don't notice it, whereas on my 45 the clear silicon had turned a funky bluish colour from meds used long ago, and was very noticable. Just a thought.

the problem i found with using silicone II is that the container says that it should not be used on aquariums. does this mean a possibility of toxic leaking in to the water? I've heard different answers about this. I am rebuilding my tank and originally I have intended to use clear silicone I but I have chipped some of the edges of the glass so I may switch to black silicone but the only one I found was GE Silicone II.

Also, anyone know a real easyway to remove the silicone between the glass as it is impossible to fit a razor or anything in between. I put some WD-40 on it and I'm going to let that sit over night as it actually seemed to work faster than the paint thinner I used.