I wouldn't be so quick to diagnose a bad starter. Can you be more precise in your description of the symptoms. It's possible that you have dino oil in the car and the thick oil in cold weather is slowing down the speed at which the starter can crank the engine. What weight and type of oil is in the engine? Are the glow plugs functioning?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13