Did the current owner say what caused that crack? That is an odd place to have that happen if it happened while sitting on the stand. If something hit the tank on the stand or it happened while moving the tank it would make more sense. I see the hole and if done correctly that should be a good enough place for the run to terminate. If I was doing the repair I'd look for any other damage in the area, make certain the seams are still bonded. Clean the area very thoroughly, use a shop vac to suck white distilled vinegar and then water thru the crack to clean it. I'd put tape over the crack on the outside of the tank, stand tank on end and from the inside I'd use #3 along all the seams,and in the crack, it has the viscosity of water so if there are any voids it'll find / fill them. I'd repeat the process from the outside of the tank with # 3 to more so fill the crack. I'd use something thicker like # 16 to fill the hole. Because this crack is in such a high stress area, I'd bridge a piece of acrylic over the cracked area , overlap it by several inches and use 16 to solvent weld it in place. it would be a good idea to do this on inside and outside of tank. This appears to be the left rear of the aquarium so the repair would not be very noticeable. Do not use silicone to make repairs, it doesn't adhere real well to acrylic. The acrylic cements such as weld-on dissolve the acrylic and "melts" the pieces together for a much stronger repair.