To add to mr. Speednjay's list are plug wires, cap, rotor, spark plugs and sometimes ignition coil (later m104 have coil-on-plug ignition), m103 timing chains wear out by 140k miles, early 104 motors like to break the EZL and used working ones are worth a lot of money, fuel injectors, if k-jet then the EHA valve can go sometimes, head gaskets don't last 100k on m104 and m103 gasket is a little better but not much. Fan bearing brackets like to go too on both motors.