A small break like that in a headgasket should cause such a coolant leak as you described

When you rebuilt the motor did you torque the bolts in the right sequence?

As for the specs measure what you got and put it agianst mercedes allows.

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)