Without much to base it on, I'd say these are totally separate issues. The fan clutch is a fluid drive that has been used for decades. The E28 has it and their failure seems to be unrelated to radiator neck failures. The necks can fail catastrophically whether they have ever been apart or not. It is purely and simply a poor choice of materials for the application. But I'm puzzled by your reservoir cracking. Usually, it's the radiator tank itself.