In my opinion the biggest reason for doing a complete cooling system refresh vs the piecemeal approach is that the cost of the additional parts and labor is small compared to the cost of having the weak link fail and potentially cause additional damage to the engine or car. There are several known upgrades for the cooling system which by its design has several weaknesses, most notably the use of plastic on critical parts like the radiator end tanks & thermostat housing. Using BMW Anti-Freeze is another consideration, use of a generic Anti-Freeze is not recommended due to the multiple types of materials used in the cooling system. My approach is too, do it once, do it right and enjoy!
