I'm wondering if this is defective leather that is not breaking in but breaking down.
Now I'm a pretty devout Brooks advocate, but I have heard of some problems with
Brooks, and if memory serves the B17 in particular.
I've never had a problem with sweat, nor proofide. What I do know is a problem is
if you ride it in the rain,and the UNDERSIDE gets wet from spray/rooster tail. Wet leather
will stretch and sag. I don't think tensioning will fix a stretched out saddle like this. . .
be interesting to hear what Brooks says.
Who did you buy it from?

Marty