My hotpoint 'first edition' shower?

Hi, When the unit is turned on and the water solanoid is opened there is a leak, dripping, from the central located heater adjuster unit from a joint at the back. Is there an 'o' ring seal or could it be something else? Do you know where I can get a schematic of this unit as I haven't managed to find one? The make is a Hotpoint and it's named as 'first Edition'