[Martin Y]

For coolant to get that far up, I would suspect it's leaking from the water pump and then being thrown around under the covers by the timing belt. I seem to remember the pump has a weep hole in the casting halfway along the neck which the shaft fits into. So if the pump water seal is leaking it'll drip down onto the crank pulley and the belt.

Do you know how old the water pump is? They're generally worth changing with every second timing belt change.