Smoke coming from center interior vent

[dog2bert]

What is the torque spec for the valve cover?

[Cubieman]

10nm

[dog2bert]

Might be the sensor at the back of the block

[Cubieman]

Might be the sensor at the back of the block

Cam position sensor maybe? This would be the very back of the head though (not block) on the passenger side, that would be the exhaust cam position sensor.
Exhaust side is accessible, intake is not w/o taking things apart. I believe you can simply buy a replacement oring if its just a leak.

I suppose the Exhaust side sensor would have more leak potential than the intake side due to the "slant 6" nature of S54.