Audio Fuse Metal fatigue

I will not discount the guys that have seen improvements with changing fuses, but it has not been my experience. I'll just leave it at that.

That just does not make sense.  Like other said, I think he's trying to scam you into repeat buying of the fuse.  If it was metal fatigue, then that would apply to anything in the unit that contained metal.  The only fatigue that one might discuss is the fatigue from the metal spring of the fuse clip/holder.  However, if you have a good fuse clip, this should never be an issue.

I do not have a dog in this fight, but you may learn something from this post.

I've the original fuse in a 1959 tube power supply. 

I would say he makes sh** fuses and buy another brand