They are notorious for leaking around the said half moon seals and cam cover gasket.

When fitting it's best to put a little bit of sealant on 'the half moon' seals.

I have the exact same issue as you and suspected the cam seals (again common).

I replaced the inlet one but still have a slight leak running down to the dizzy which I suspect to be the 'half moons'.

It's as said though it may well look to be coming from the HG but it will be coming from one of the places above, and running down.

Martin