I've traced a coolant leak, seems to be coming from a black steel pipe that runs under the manifold, where it meets the engine block - might be a perished seal or O-ring??

Anybody had this before, or removed this, I'm hoping I won't need to remove the front bumper or manifold!

Yeah got that pipe off with manifold in place, cleaned and re-sealed, just topped coolant back up, bled until all air out, and is now running sweet!
No overheating, no more leaking.

For those with the HGT, the pipe is cast aluminium and cant be removed with the exhaust manifold in place. It often leaks at the cam belt end when the bolts have not been done up evenly. Its an easy fix (ish), but scary because the coolant comes out from the cam belt cover making you think its the water pimp leaking. That cover is a barsteward to remove.