Not trying to be argumentative at all, but lots in that MFK thread has changed. The GE construction adhesive is now Momentive, they aren't called GEI and GEII anymore and I think even the Dow products have changed. And the price gap between the GE sealants and the aquarium silicones has shrunk. When the GE sealants became popular, they cost $3 or $4 per tube at Home Depot and the handful of websites offering AGA silicone wanted $10. They cost $6 now and you can get aquarium silicone tubes from Ken's and others for $8.
If it's a known leaker, I agree 100%. Tear it down. By the same token, consider what's you'll get in return for your $25 worth of silicone and 3 or 4 man-days (if you've ever done it before): a 55G with thicker glass than the Tetra tanks Petco sells for $55. Just offering a line of thinking here. A leaking 210G for example is another animal altogether.
Just curious why the cube wasn't a workable idea for you? If I was gonna tear down a tank like that, I'd sure give that one some consideration. A rimless cube isn't cheap to come by.
"Why can't my wife see all of this stuff as an investment?"