Hi Cptn
Just to add a bit of clarity here, these valves are not YOUNGS valves, they are standard valves that are fitted to all the basic and king keg barrels, regardless of who the wholesaler/supplier is that puts their own label on the barrel.
One manufacturer produces the barrels, Youngs, Ritchies and Hamb bards all sell them. All three offer the basic barrels with plain vent caps and all three offer the facility to buy them with S30 valves or pin valves. All the valves are supplied from the same manufacturer as far as I am aware.
There is not, inherently, a manufacturing problem, however the valves are fairly prone to this type of discolouration if left in sterilising solution for any extended period. Normal Sanitising doesn't harm them in any way, but if you put the sterilising solution that you use to clean your fermenter straight into the barrel and leave it to sit there (with the lid on) for the 4-6 days your beer is fermenting, by the time you rinse it out ready to accept the beer, the valve will have been sitting in a closed, slightly corrosive, environment for several days.
I know, as several of mine have done the same thing !!!! (But its a little easier for me to replace them as I just take them off the shelves from the box that Darren saw them in
)
Also, as luck would have it, the man you spoke to at Youngs actually IS called John Smith - honest
If you are visiting soon, I've got Fixby Gold (about to go off), Muntons Gold Highland Heavy (about to go home) and Nelsons Revenge currently on as taster, with Santas Winter Warmer, Colne Valley Bitter and either Black Moor Stout or Muntons Imperial Stout about to go on as replacements. :
Andy