It sounds like a cracked head or a head gasket problem.

OR

The overheating is what caused the engine to need a rebuild.

Did he hone the block and ring the pistons? If so, throw the engine away and install a new one. You can't hone the cylinders on that one.

Good luck/

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Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS