Again I want to thank everyone for their kind comments which have inspired me to keep going and please excuse my lack of direct response.
Well I changed my mind (not the first time) and decided that while I still have the aquarium upside-down I might as well put on the bottom trim which had arrived by UPS the day before. Sorry no pics yet, I'm working alone today and with sticky silicone fingers picking up a camera doesn't work, but the pics will keep coming as I finish a segment.
The trim is not standard aquarium which cost way too much IMHO. Rather I am using black PVC 1/8 inch thick angle iron which is much much stiffer and much more reasonably priced, a 1.5x1.5 inch right angle section 1/8 inch thick and 6 feet long cost about $7. You can buy it in different lengths, thickness up to 1 inch and angles up to 4 inches on line and shipping is very reasonable.
But after this hands on experiences I have really learned allot about the relationship between glass and silicone and why plastic trim no matter how string can never really be anything more then a decorative item, and that is becasue of its poor ability to adhere to silicone. Apply silicone to clean glass and you have to use allot of effort to get it off once cured. In fact without tools like razors and sand paper its almost impossible to get silicone off glass with your bare hands. But put some silicone on any piece or type of cleaned petroleum based plastic and after it cures (glass not involved), you merely have to peel up the leading edge with your fingers and it peels off like electricians tape. Of course with a large surface area like trim it stays put mostly becasue of the silicon sticking to the glass so well. So there is a part of me that regrets not spending $20 more and using aluminum angle which had sealing properties almost as good as glass to silicone, this would have provided a structural double seal. Live and learn.
iap- All I can say is that replacing a panel is relatively cheap especially on a large aquarium. You have a choice, you can trash the 240 gallon and buy a new one for $800 or find another used one for $250-$400 after waiting 6 month to a year and a possible hidden crack, or you can order your own glass for about $120 plus incidentals like silicone and razorblades ($30) and do it yourself. But unless your willing to be extremely persistent, yet patient and self motivated about the opportunity learn and experience something new and the conquest involved, otherwise it may not be worth it. Your biggest enemy will be your confidence and having to learn new skills in what seems like an impossible task, turns out to be very rewarding just like learning to drive a car or swim.
Now that I know how to do it, I would definitely do it again. In fact if I am ever in the market for a very large glass aquarium, I will definitely be looking for one with 1 busted panel which should make it a super bargain maybe even free LOL