If you can apply the emergency brake while the car is slightly rolling and not get the sound/feel of metal to metal contact, replacing the shoes probably won't do anything. The only other possibility would be that there is oil on the shoes, but how could that happen? There is no axle housing to transfer the lubricant to the shoes like a typical American car.

Is the cable assembly okay? Is the pedal feeling tight with only 5 or 6 clicks down from the top position?

Good luck,

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Larry Bible
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles