If it has the loop type plugs, I'd replace them with pencil plugs. It's simple and they start much better with pencil plugs. You'll need the retrofit pencil plugs, not the standard pencil plugs. Threads on here with part numbers and instructions.

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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