Aqualisa Pwr Shower - leak from cartridge gasket

[converse]

Our Aqualisa Aquastream (97-03 model) pictured here:

http://www.aqualisa.co.uk/parts-sto...hermostatic-and-manual-integral-power-shower/

has a constant leak from the gasket (between the cartridge and main unit), dripping slowly into the casing. It's happened on and off for the past few years, which has rusted the bottom two screws holding the cartridge in place, and results in a drip from the casing into the shower trap and a nasty build up of limescale in the casing at the bottom.

The gasket seems absolutely fine - in fact looks as new, I'm certain it is definitely leaking from the gasket area, so will silicon grease improve it (or is it useless?), or should I go for some sealant around it, or...? The leak over time causes the microswitches to fail, and I've already replaced them twice in the past 4-5 years.

Any tips? Other than this, the shower is fantastic, had it since approx 2001 and we have at least 2 showers a day with it.

[edited to add about microswitches]

 

[seco services]

Check the plastic valve body they can be prone to cracking and leaking.
Also check it's not from the cartridge and running down under the valve body.

 

[converse]

Thanks seco services, think you might be right about it coming from the cartridge itself...I've had another thorough look this morning and put silicon grease between the gasket and the cartridge and replaced two of the rusted screws just to make sure it's a true water tight seal...

It doesn't appear to be leaking from the white valve, in fact no leaks at all, until you turn the water on (via the control knob), and then it starts to leak from the grey part right at the front of the thermo cartridge, I assume it's leaking from between the grey and black section. (The grey section has the brass screw holes to which the temperature dial is attached), pic below:

http://www.aqualisa.co.uk/parts-sto...integral-power-shower/Thermostatic-cartridge/

The water then drips backward and makes it appear to drip from the gasket.

So... now I assume I've finally traced the actual leak - is there a seal/gasket/O ring that can be accessed and replaced within this section of the thermo cartridge (if so does anyone know how to access it), or does it require a completely new cartridge at £100 plus?

(Last thing I want to do is buy a new one, and find it's still not right!)