Warning: Stop using WD-40 as a chain lube, I learned the hard way on a customer's bike

Did you ever check if the WD-40 was actually getting into the pins or just sitting on the plates? That stuff is mostly solvent, so it strips whatever lube was left and then flashes off, leaving the chain dry as a bone inside where it matters. A $10 bottle of dry lube and a $15 chain checker will save you way more than three snapped chains and angry customers.