I would not trust it. We have a lot of old Brooks saddles in this house -- some came on old bikes, some we bought to put on old bikes -- and not one of them is safe or comfortable to ride. If a Brooks is treated well it can last a long time, but people don't sell old Brooks saddles that they are treating well, and once an old Brooks stops being cared for, they fall apart pretty quickly.
I had one that looked very much like that, except someone had dunked it in Neatsfoot oil so it was also slimy and gross right over the cracked leather, and on my second ride I was truly riding on the frame. It was miserable.
My husband had one that looked mostly fine, but it broke in the middle of a ride. It had been overtensioned and over-oiled, and the whole nose part of the leather just snapped off, leaving him to ride home standing up at 2 a.m. Kind of the wrong sort of Saturday night excitement!

