I think tailcaps are more or less akin to lamp assemblies, in that if it's a bad one, it will fail very early on. Therefore, if you've had yours for a while without any issues, I'd say you can be pretty confident it's going to continue to function properly. I don't want to spark yet another SF clickie thread, cause gosh knows we've run that one into the ground, but personally, I think it's a minor issue. I've had over 20 SF clickies without ever a single problem. There are several members here that have been less satisfied that I with them, but I think overall, what we perceive as a 'mass clickie malfunction' is rather a product of a vocal minority compared to a satisfied, but silent, majority.
I may be off base here, I'm just basing that off of my consistently good luck with them. Others may tell you otherwise from their own experiences.
Now, about SF customer support. I've called them twice. In my experience, they can be somewhat spotty with email support. Calling them, I think will yield better results for you. They have never asked me to provide proof of purchase. As far as I know, they will warranty any SF light, regardless of how many owners it has had.
Enjoy your U2, mine is my favorite light.
