If the Vanos seals are leaking you can have low oil pressure at idle, especially hot. Try adding something to thicken the oil a bit like STP just to help with diagnosing the problem.
Typically though, the light will flicker at first and get progressively worse.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)