Sorry to hear that man.
As to re-sealing it, I just did a 55 gallon and it was easy.
I went above and beyond when I did it and made sure I got every last piece of silicone out and then some. I went thru about 5 razor blades, and then I taped off the area around the seams with enough of a gap(about 1/2") to allow silicone.
Just do one section at a time, don't be shy with the silicone, wear rubber gloves and when you have the silicone in between the tape, start at the corner or bottom and run your finger up or sideways depending which seam you are doing.
Once you are done remove the tape, and let it dry. Use acetone to remove any unwanted silicone.
Wait 48 hrs before adding water and then another 24 hrs before adding fish
Make sure you are in a well ventilated area as using this much silicone it will start to burn your eyes and stink to high heaven
Any questions ask away, as I am very Diy and cheap LOL
good Luck and again sorry to hear about the leak