I’ve used Brooks Flyers and more recently a B67, and they all produced a lot of creaking, masking other bike noises I want to be aware of. I’d oiled the springs and Proofhided the places where the leather is over a metal surface. All of these efforts produced minor or very temporary results. I recently ran across an older blog on a touring website that made a real difference for the B67 I’m now using.
The blog recommended inserting a nylon washer at point A, between the nose of the rail that attaches to the upper end of the springs and the metal flange that is part of the fitting through which the tension bolt is threaded. Instead, I inserted a small square of dense polyethylene (cut from a windshield washer fluid bottle) at point A. That made a big difference, but there was still some noise, so before the next ride I used WD 40 spray grease on points B, taking care to avoid overspray on the underside of the saddle. That silenced the saddle. I put 40 miles on the B67 today and heard only silence.
The triangular rail that attaches to the upper end of the spring is subject to rotational forces as I pedal, and the noise apparently resulted from the torque at point A and vertical movement at points B. Inserting a nylon washer at point A may be the best solution, but I think it might require partial disassembly of the spring attachments to make the insertion, so I used a thin, dense polyethylene strip which I could get into place using a small screwdriver as a wedge to separate the surfaces at point A. The grease at points B may have be to be frequently replenished, and perhaps even the polyethylene strip, but I’m OK with that. And altogether, there may be other ingenious solutions. But identifying the source of the problem was a Godsend.