My 82 and 85 has 21 mmHg and 22 mmHg respectively with the brake line plugged.

I agree, you are in the ballpark.

dd

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car