With my Lincoln, that would be normal too. Loved that it also took a full gallon. I thought I had a leak too. But I never find any fluid dripping and like I said, level stays the same for days on end without use. Also, the tank is newer. I think the PO replaced it. Nice clean plastic.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car