More of this well trodden path

My coolant alarm gave a chirp yesterday and indeed the level in the header tank had dropped a little. Not too much. Topped up with about half a pint.
Left overnight and no sign of an easily detectable drip.
Took for a wee drive to heat her up and then back for a close inspection. Header tank still appears full but don't want to take the lid off, as its warm.
Good look about with a torch. No obvious leaks but I have found a wet end to a rubber pipe under the radiator where it inserts onto a small metal pipe. I've done my best to take some images but it's not easy to photograph down there!
https://flic.kr/p/X8v8Zx
https://flic.kr/p/WSJsNL
Could this be the culprit?
Thanks as always,
Colin