You can purchase a warranty from a third party, thats what I had to do with my 01. Only problem is they really only cover major repairs, and not fairly minor stuff.
Heritage is a good company to purchase from, but i dont know how to get a service contract from them without going through a dealership... they have no website, but i could provide you with their phone # if u want.
Perhaps your BMW dealership offers a 3rd party warranty?
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