When you say "low" after running on the highway, was this while you were driving it dropped or at idle? I have found here in CT with the cold temps we have been getting, that the oil has a higher "warmed up" pressure. By that I mean, after running on the highway and then coming to a stop, the pressure would be up near 2 Bar. I believe the owner's manuals say that it can go as low as 1 Bar (at idle) if it's hot out and you have been drving high speeds. I don't think you have anything to worry about.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member