Expansion tanks failing is a very, very common thing for most BMW's.

Your mileage will indicate what you should do as far as hoses are concerned. However, from personal experience and everything I read, once you start replacing components on your cooling system it stresses the old components you don't change and they start breaking as well. Probably best to replace the entire cooling system if you have anywhere near about 90k miles or so. I would use OE parts, but that is up to you.

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Profeshenal spellar