The low coolant light came on and it was very low, after filling it about a week later it was at the same low level. I've looked at it running hot and can see no obvious leaking anywhere and nothing under the car.

I did notice red crusties at some of the hose termination points. So is it boiling off at those locations? I noticed someone put a regular hose clamp behind one of the norma clamps from the reservoir, otherwise the original norma clamps are all intact and there are no crusties around most of them.

 

The common leak locations on an XK8 are the thermostat housing and the Norma connectors on each side of the engine. All will tend to leak slowly and dry up due to engine heat. Dried, crusty red/orange deposits are, indeed, signs of a leak. The thermostat housing leaks onto the top of the engine under the intake manifold and evaporates. That can also destroy the knock sensors. The Norma connectors leak drips onto the catalytic converters and vaporizes. A leak at one or both of the Norma connectors can only be fixed by replacing the octopus heater hose . . . or by cutting the connector out and using a standard piece of 5/8" hose in its place with screw type clamps.

 

The heater hose/octopus hose is fine no visible crusties or leaks at any of it's visible connections.

The problem hose is between the filling reservoir and the thermostat housing as it has red crusties at both ends. The hose doesn't leak so should I just replace the clamps at both ends then? Have to figure out how to post pics here as I have a couple!

 

There is some new-guy restriction against posting pics, but I think that goes away at 10 posts. If so, you have arrived!

Anyway, yeah, why not just replace the hose and clamps where the leak evidence appears? That may be all you need.

 

You also might want to get a loaner coolant pressure tester from Advance Auto or Autozone. When you pressurize the system, you will then usually be able to locate the leaks by looking for bubbling and hissing.