This tea is three and a half years old, by my reckoning, so the flavour is starting to go. That normally makes for a particularly pathetic cup of tea. But today it turned out pretty well.
What I did was use more leaves (probably 1.5 times as much as usual) but brew it exactly the same (1 min using 80 degC water).
So, until I hear anything better, my solution to old leaves will be to use more leaves and treat it the same otherwise :-)