It's not repairable. Once the wall thickness rusts through, any attempt to repair it only weakens it further. It use to be water heaters had a thick gauge metal used for their container. But over the last 20 years the thickness has been reduced for cost savings. With the thicker tanks you could patch them. But not any more. The cost of a water heater is relatively cheep and the installation time is only about 1-1.2 hr. When you call someone to install it for you, you can reduce your cost, by having the water heater completely drained. In addition, make sure they don't charge you by the flat rate. Flat rate pricing is based upon 2.5 hrs of labor. Find out the hourly rate and have them charge you the travel time (standard) and the time on the job. If you do, your charges will be less than if you accept the first offer. Go to one of the Home Depot stores and pick up the water heater yourself and have it ready for the plumber. Dispose of the old water heater yourself. If you do these things instead of a $700 -1000 dollar bill, you will have a $400.00 bill.