I'm curious to know if a used Brooks saddle have to be replaced by a new one..
If yes, how can we know ?


Thanks in advance
You'll know when the one you have gets uncomfortable.
Except it's likely a boiled-frog thing. It might be hard to remember how much more comfortable the saddle was when in better repair.
When I bought my Mercury, I fitted an ancient Brooks Professional that I had acquired from a bike purchased used 40 years earlier. I'd revived it with a soak in neatsfoot oil and had used it happily enough on several multi-day tours. I had preferred it to various plastic saddles I'd tried.
With the Mercury purchase I was in the saddle much more frequently and for longer periods. I started to wonder whether a new B17 might be better. Took me a while to male the jump because I'd heard the horror stories about the discomfort of a new Brooks and the need to accommodate that for a thousand miles or more while it broke in. If it broke in.
Bit the bullet and on went a standard B17. First ride it proved exactly as comfortable as the ancient Professional it replaced, and hurt in just the same places.
It's now been under me for a couple of thousand miles (guesswork as I don't use a cyclometer) and it's fabulous. Way better than the old one, which is the point of this anecdote.
It's a real pleasure setting off on a ride and feeling the comfort of the broken-in Brooks underneath me. For the next couple of hours I don't even think about it. At that point if I've not been off the bike or much out of the saddle I may want to stand on the pedals for a bit of relief. I'll only need a few seconds.