I would go with the diesel if it's as advertised - check it out, ask to see any books or records that he's got, drive it on a freeway to see how it goes down that road at speed.

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Houston, Texas
1984 300CD 235K miles, Elvira, one owner
1987 300TD 180K miles
1974 TR6 78K miles Sarah Jane, one owner
OBK #27