I'd take a good look at the two hard plastic cooling pipes that enter just behind the oil filter housing.
I saw some residue there during other repairs and for a long time was trying to find a slow leak in the cooling system.
When I did the head gasket, I changed those two and the ends had degraded to the point they were weeping coolant just fast enough to evaporate but not drip.

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2001 x5 3.0 (sold with broken motor), 1990 e30 M3, 1991 318is, 2002 325i, 2008 335i Dinan stage 3 6 speed,