Donut gaskets

[DAVECAD2.0]

'91 420SEL.
When replacing the donut gaskets between the two intake manifold halfs do you tignten the two halfs until the stop bosses contact each other? Couldn't find anything specific in the FSM, torque, etc.
Also, what is the function of the loose ring around the middle of them.
TIA, Dave

[mbdoc]

The actual seal for intake halves are in the center of each of those "donuts".
Each side of the intake squeezes on that sealing area,
Torque to 8-10 ft lbs.

I believe MB said that was for heat dissipation. Early versions did not have them.

[DAVECAD2.0]

Thanks MB Doc