The Sierra Click has been my favorite pen kit for a long time. The mechanism was changed 2-3 years ago, as you would know, Harry. . I can explain the change if you wish.
Very recently I had my first problem with the new style kit ... the click mechanism did not operate reliably, in the sense that the refill would not properly retract all the time.
Actually, it may not be the fault of the mechanism; it may be the fault of the kit-supplied refill, which may have a wider than normal tip on it.
I corrected the problem, I think, by enlarging very slightly the nib opening. I did this by carefully selecting just the right size numbered drill bit and gently forcing it backwards through the nib hole. Note that I was not using the bit as a drill ... just as a "rod" only *very* slightly bigger than the nib hole. I think it was a number 37 bit.
Perhaps this action simply flattened a tiny burr on the inside of the nib hole.
I should have tried a high quality refill (Schmidt or Private Reserve) first of all but I didn't.
Time will tell if this has been a permanent fix.
I will be carefully monitoring my use of the Sierra Click kit in the near future as I make more pens of this type.