Acrylic tanks are almost never finished
my 450 exploded in someones house due to a poor stand and i repaired an entire cracked bottom and seperated back wall. Tanks been running for almost 4yrs now. Urs sounds like a minor fix. #40 does wonders when refurbing acrylics. 
Dang I didn't know weldon turns yellow over time... definitely still better than scraping a tank altogether but I wonder if it would look better using acrylic rods in the corners with thinner beads of 40. How long does it usually take to start yellowing and would going thinner than 1/2" still prevent future crazing? Fedex delivered my gallon a few weeks ago and the part A is already pretty yellow but I thought that was normal lol, the nearest place that carried it was 6 hours away tho so maybe they sent an old batch...
Believe me i understand, im in the same boat. My 3k should have been finished months ago hah
Ive used acrylic rods aswell up to 1" on the inside seams and i prefer the look of weldon even if its yellow buts its all personal preference. Both methods work under the same principal. Even if ur weldon arrived yellow it will clear up when u add ur hardener. Acrylic itself will yellow with age just the same and 20yrs is a long time in my eyes.
I highly recommend working in a garage or heavily ventilated area aswell as using a respirator mask. Ull be on the moon before u know it lol....it can be hard to move large tanks and ive had to do a couple in my basement and the smell of the glue was a nightmare for a few days.
I'm probably gonna have to do it inside of my apartment because even if I convinced someone to help me move it downstairs I would still have to keep the garage mostly closed to make sure my apt manager and neighbors don't see an 8ft tank in there lol. I was planning on getting a good mask and keeping all the windows open with a fan blowing out but I'm not sure if that will be enough to protect our dog and cats. Im hoping the actual tip and pour process only takes a few days so i can just keep them in my room with the door closed. That stuff smells pretty strong without even taking the lid off tho so I can't imagine how bad it will get while pouring (especially with my head inside the tank lol)
Ive done the same with the mustard/ketchup bottles...its hard to rush through and get everything glued in the 20-25 min potlife. I thought i mentioned how hot it gets lol my bad...glad to hear everything else went well tho, id say that seam is good for another 25 yrs now
