I have 4 Brooks, the oldest one, a Profesional, is now more than 30 years. I still using it on my new folding bike. Never have such problem nor have to adjust the tensioning screw. I weigh 73 kg (160 lbs) and use them in the tropic in the rain some times.

What model is yours? The cheaper models use thiner leather. Or maybe they don't make them like they used to!