The e39 and e53 sit side-by-side in the garage which is LEVEL. In 8 years I never encountered this with the e39 or the e46 for that matter.

And I use rarely the e53, so every odd morning before I leave to work, I have the habit of checking all kind of fluid levels. Some time I check on the e53 as well.

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Stable: e92is, e46 M54B25, e83 N52, e53 N62 - sold, e39 M54B30 R.I.P.