Anybody know about fuel sending units on C230 ??

My fuel gauge is whacky, so after a post here I learned that my problem is most likely to be the sending unit in the tank. I discovered that this model has TWO sending units. Would any of you be
so kind as to tell me your advise on whether one or the other is inherently faulty on this model, or do I need to just buy both and not worry about this?
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