WD 40 will attract dust and fine dirt, making it all that much harder to clean, and it will get dirty faster. When you wash your truck, lift the hood and wipe the motor and engine bay down with a damp cloth. Keep it clean, and that's all you'll have to do. When I had my Mach, and with my 65 Mustang, I detail the rubber parts like hoses, vacuum lines, etc. But I use 303 Protectant, a product that doesn't attract dirt like WD does.