Most Brea homes run a gas tank heater in the garage or an outside closet. The city's water is hard, so each gallon you heat drops a little mineral on the tank floor. Years of that sediment make the burner run longer, make the tank pop and rumble, and give rust time to work through the steel from the inside.
A failed part is a repair: a thermocouple, a flame sensor, a gas valve, an element, a drain valve or a relief valve. A leak from the tank body means a new heater, because nobody can patch steel that has rusted through.
A California replacement has more to it than a new tank. The heater needs earthquake straps, a correct vent and gas connection, a relief line that ends somewhere safe, and often a city permit. Check with the City of Brea on the permit, and check any plumber's license at cslb.ca.gov before work starts, ours included.