Coolant Leak

[ONF]

I've noticed recently that I've got a slight coolant leak. It's not much but the level drops slightly every few hundred miles. I tried to find some sign of the leak (carpet in the boot is dry etc) but found nothing until this weekend when I finally found a trace of the leak.

It seems to be dripping onto the chassis support by the right rear wheel around the point of the fourth bolt I've circled in the picture. You can see where the coolant has stripped the paint off the metal on the support on that side of the car. I can't see where the leak is coming from though, I can only work out it seems to be seeping onto the top of the chassis support at that point circled.

Any idea where the leak could be from? To give you an idea of position that fourth bolt circled is roughly in line with the centre of the rear wheel.

Thanks