Leak on a Ford Transit?

I've just bought a 2.5i diesel Ford Transit (1988) and there's a water leak which is seems to be coming from the aluminum housing (which I don't know the name of!) behind the water pump.

It's a very slow leak, could it be coming from anywhere else? Could it be a faulty water pump or the gasket on the housing and does the timing have to be re-set if the water pump has to be changed?

Having a look I can see the water pump is a nightmare to get to. There's just the one bolt which I can't get to as it's behind the rest of the engine. Any tips?

Mark
markandchrisuk@gmail.com