Go to this website
http://74.125.47.132/search?q=cache:VwLkVqyHhl4J:www.boschhotwater.com/LinkClick.aspx%3Flink%3DTechManuals%252FGL_English.pdf%26tabid%3D650%26mid%3D2003+ariston+water+heater+maintenance&hl=en&ct=clnk&cd=4&gl=us
and read the page on troubleshooting.
It says the most likely cause of leaking is the seal between the heating element and the tank.
I haven't pulled mine yet but there is one screw to remove the cover and four nuts to tighten (or to remove to inspect the seal and then replace.)
Remember to unplug the heater before removing the front cover.
Karl
January 2009