I've seen mine show full and within the same week, it will show 1 bar low.

What I thought was weird is that it showed full when cold but iirc, oil expands with heat. My thought is that the oil is up in the cylinder head so oil level is lower in the oil pan. Makes sense I think.

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e70 - purchased 6/2018
e36 - wouldn't pass smog at 190k 2016
e53 - transmission blew at 225k 2012
e30 - sold as it was a little slow for a DD and burning oil at 220k 2011