Lots of miles on a Brooks B-17. Ordered a third one for a new bike, but was shipped a Swallow instead. (Costs twice as much but they said I could keep it.) B-17 is comfy for me right out of the box. About 1000 miles on the Swallow now. Still not comfortable, but usable. The B-17 offers more support. The Swallow is narrow, and purposely less giving from their tying the aprons together underneath. My bars are almost at saddle height, so the B-17 is fine. If I had bars 3-4 " below the saddle, the Swallow might be better.

I don't treat any of them. One went 52,000 miles until the bike was stolen. If it's raining, I'm the rain cover. But, too, I don't leave them parked out in the rain, either.