Gasket was in perfect condition (Elring), used new headbolts, 2 perfect 90 degree torques after 70nm tighten, head was resurfaced etc....... I just don't want to believe that this is the cause. Maybe another 90 deg torque down could solve it, who knows. Anyhow, it's at the shop being diagnosed. I'll report back when I find out more.
Thanks for the responses..
'91 300E, 208k miles