The problem with repairing a tank is that you cannot get a good bind or seal applying new silicone over old silicone. So in order to do it properly, you would need to strip the old silicone completely and reseal. Otherwise you will have an accident waiting to happen.
Silicone is the primary structural component and sealer. The trim is secondary, and in some cases strickly aesthetic, depending on manufacturer.
If you reseal it, make sure you get a high quality, aquarium safe 100% silicone. Make sure it has no additives for mold inhibition. The best aquarium silicone I know of is GE RTV, but you may have to search for it.
Just remember if not done properly, you could have 90 gallons of water in your home, probably at the most inopportune time.
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