Just be careful... I had an old Dayton of London leather saddle which was very dry and dirty. After cleaning it I proofed it with Brooks proofhide and re-tensioned it, all went well until the leather started to split away from one of the nose rivets after a couple of rides.
It was no doubt my fault as I may have overtensioned it, if I was doing it again I would leave the tensioning alone for a few weeks to let everything settle down again as the leather soaked up the proofhide and regained its flexability.

385xza