I recently made this shader as a procedural surfacing exercice for students at UCP. After perfecting it a little, I'm now making it available as CC-0.
The shader includes 4 main components: wood, grooves, stains and dust, with color inputs, scale inputs, roughness settings for the dust filter with dust accumulation in grooves. Stains and groove roughness and bump settings are independent so you can add some rough stains or grooves without diffuse color for example.
The shader outputs standard PBR maps for the Principled BSDF as well as a clearcoat normal and a displacement map with only the height information from the grooves.
There are several settings examples included in the blend file, but with only a few tweaks, a lot more is possible.
Thank you for your interest and happy blending!