Finally...

...I've got round to fixing the "pet annoying little job"... the bad earth on one headlight.

Its so nice having full power from both headlights, I'm tempted to go and drive round in the dark to enjoy it.

Judging from the state of the headlamp plug (mildly melted) it seems the earth lead had partially fallen off, then got very hot and rusted. I've cleaned it all up, tightened the crimps and put it back. That of course took 30 seconds, dismembering the headlight bowl enough to get at the offending connector took about 15 minutes. Last time I did this, I just pushed the plug back on, and it went back to being dim about 10 minutes after I started driving... hopefully now I've tightened the connectors its problem solved for good.

I had a mild panic after doing the headlight; I checked the water level in the radiator, and found to my horror an oil emulsion on the bottom of the cap. Halfway through a prolonged effort to see if there were any bubbles in the water the penny dropped - guess who had used old 3L veg oil cans to transport the water last time he filled the radiator up, and not washed all the oil out first. Panic over (I think, I'll have to keep a bit of an eye on it to check just in-case there is another cause).