Thanks for that Lee.....I had the same problem on mine, but it was only badly corroded but was the cause of my loosing coolant. This does appear to be another common fault (another one
...surely not). I do know of a number of these that have failed. It does appear that the corrosion starts after a number of years due to the deteration of the hose which causes the coolant to weep through and when it meets the air, pitting occures which eats away around its junction with the main body. Mine had not corroded through fortunately, so I was able to clean it right down to the alloy and with two pack epoxy build it up back to original plus a bit keeping the original profile. I then slipped a length of adesive heat shrink over it right up to where the vacuum valve sits...applied a hot air gun, and now the coolant goes no where near the external alloy. It has only been on for a few months now and around 300 miles covered, I took off the hose to check a week ago, and it all appears OK.
Pic shows repaired unit prior to the heat shrink being applied.
1990 GTA Atmo, 2003 Jaguar X type 2.5SE Auto, 2018 Kia Picanto GT-Line-S 1.25