Powercraft 7944 pressure washer leaking seal?

Water is leaking from the bottom of the main unit. I've taken it apart and the leak is due to a circular rubber seal being split (I think it's called an O Ring). It's just before the 90° elbow that projects out of the front of the machine, where the hose connects to. I tried to put some rubber gasket sealant on it which worked for a few seconds before leakng again. Does anyone know where I can but these O Rings from please? I have been told that Karcher keep spares for these, but they say they don't, even though they get asked for them lotsvifvtimes. Can anyone help please?