The Reich mixer tap in my caravan was leaking from the top even when the tap was not being used because the water system is pressurised (no microswitch, no wires).
The problem was not due to the rubber seal (3 joined rings - like a face) but to wear inside the cartridge itself.
Got a new cartridge from liesureshopdirect.com (about
£12 incl postage) - problem sorted!
PS. Clean out any scale or other deposits before dropping the new cartridge in - but DON'T use anything that might scratch or score the soft brass housing where the seal sits.
PPS. Don't over tighten the ring nut or you may distort the cartridge. I found that finger tight (hard as you can) then turn one more "flat" with a spanner was enough. If in doubt, under tighten it then gradually tighten until leaking just stops - and then just a LITTLE bit more to make sure.
Bruce Beard
August 2008