Approved antifreeze and corrosion inhibitors

Coolant additives: 

Aftermarket coolant additives are not approved by BMW, including but not limited to those which provide additional corrosion inhibition or seal off minor leaks are approved by BMW.

Use of non-approved coolant additives may cause reduced heat transfer from the cylinder head to the coolant, in addition to the formation of hot spots. This can cause the burning through of cylinder head gaskets and/or cracking of the cylinder head.