I certainly would replace it Juliem- immediately. It's not the size of the tank that determines the amount of water leaked, but it is the rate that the tank is refilled from the header tank above.
Difficult job I know, having replaced many. The pipe work positions may need adjusting but the two important things are the condition of the floor beneath the tank and the sealing of the fittings to the tank. The latter will only be known to be OK when the whole tank is refilled. Best to use the gas grade PTFE tape (which is thicker than standard) on the treads of the fittings to the tank which should all be new anyway.