I have three leather bicycle saddles. One I bought new about ten years
ago, the others I picked up second-hand.

The older ones are great - they are hard and supportive. If you rap them
with a knuckle, it feels like knocking a piece of wood.

The newer one, supposedly the same saddle from the same maker, is soft
and unpleasant, and just gives way.

Is there anything I can do to it to improve it?

Daniele