Yea, I was wrong. It is:

1. Medium thick washer
2. Circular spring
3. Thin washer
4. Thick Washer

This causes the thick washer to butt-up against the matching thick metal housing that surrounds the coil. The pressure of the 4 screws slightly compresses the circular spring to keep constant pressure on the large diaphragm to seat it in the valve body.

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Mike Frederick
1986 300SDL, 240K+ miles
1985 300D KaliKar, 270K+ miles