If there is coolant in the oil, then the rod bearings have been compromised...Even if just the head gasket failed, and he replaces it...there is a good chance that not too far down the road the engine will destroy a bearing or two, requiring a full rebuild. This happens ALL the time over on the Supra forums. The inline-6 engine used in the Supra loves to blow head gaskets, and requires very careful maintenance, and lots of attention to keep it alive.

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles