Having cured the rad leak and the water pump leak over the last year, now faced with a new leak . When cold, it leaks, when hot it doesn't. Not a great pic but basically its the last point of the drip coming past the little shocker that is just under the alternator. Been suggested that it could be the alternator O ring or a crack in the alternator casing. Any one else like to throw ideas in to the ring before all that comes apart. ? Pic taken from front of engine looking back.

If it's a BMW M62 4.4 (looks like it) the alternator is on the other side and not above that point so highly unlikely to be that.
If the water pump was changed I would check the hoses for leaking, they rely on o-rings and if they weren't changed can leak (ask me how I know).

Ummmm, your right ! Now the mystery deepens even more.

My TD6 did exactly the same after we'd done the water pump and rad.
When cold it would leak but warm there was nothing!! It turned out to be a bad seal between the water pump and the block. A second new gasket and liberal amounts of gasket sealant had it fixed in no time.

Think I've traced it to the water hose that comes from the rad to the thermostat housing ( V they have an O ring in which should be replaced when ever you've had the hose off but when I tried to buy one was told you had to buy the whole hose ?

You can't get the O-rings separately but just hook them out and buy the equivalent size. Obviously if the hose is past it's best then just get a new hose, I went for new hoses when I changed my rad.