Have you tried glowing the plugs more than once, my starting procedure for cold mornings is as follows, is double glow, then foot to floor, start cranking, foot 1/3 way down, and keep cranking till start, sometimes 20-30 seconds if its really cold and i didnt use the block heater.

It sounds like bad fuel, I would suggest cleaning the tank screen, and starting with fresh fuel from a "good" station.

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1984 Euro 300SDC, (4spd standard)
1986 Toyota Landcruiser Diesel HJ60 5spd X2

Gone but not forgotten (some sold, some stripped)
1983 300 SD, 1985 300 SD, 1983 240D, 1986 300 SDL, 1985 300 SDL, 1983 300 D, 1984 300 D, 1985 300SD, 1987 300 SDL, 1983 300 SD, 1985 300 TD Euro, 1983 380SEC, 1990 300 D, 1987 300D, 1982 300D, 1982 300D, 1994 E420, 1987 300 TD, 1987 300 D, 1984 300 D