Need to replace coolant rec tank

Okay so the tank on my 645ci is bleeding and I need to replace it. car runs fine and I have not overheated but I want this taken care of and don't want to pay $400+ to have it done for me

Can anybody give me a comprehensive breakdown of why I need and how to do it? It looks easy but I am not car savvy so I could use the help

Thanks a bunch.

Post #12 and #18 in this thread have links on how to replace the tank plus coolant add/bleed instructions.

Wrong thread. This one actually has the link for the expansion tank instructions.

Thanks.
The little pin sensor inside the tank broke off just like that poster's did - do you know the name of it?

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You need to replace the entire tank, the part that breaks is not available separately.