Look for ( in no order): Torque rods with bad rubber, puffing or lots of smoke from the crankcase vent, running on less than 6 cylinders, won't exceed 45 mph, rusted rockers and cowl, oil coming from the brake drums, really late clutch engagement, clutch slipping, oil puddles under truck after sitting a day, wobbly fan blade, lots of play in steering, severe rust in rear spring trunnion seat, exploded winch worm housing, howling from any gear cases, blue smoke from exhaust, no hum from in tank fuel pump, oil in air tanks, engine oil milky, water running out of axle fill plugs, high engine oil level, clicking or knocking from engine, puffing exhaust, pulls hard when braking.
Others??