Grimy oil covered the foundry's floors. Darkness ruled. Workers came and went before long. That was the way things were at Gunite, a semitrailer truck brake drum maker, when Jeff Clark — now director of production management — started working at the foundry 34 years ago. New hires would "come here for a day or two and say, 'What did I do?' " When Mark Bucey, senior product engineer, began working at the…