Andy,

How many miles and how long since the charging system and starter have been checked? Sometimes, as the battery ages the drain of the glowplugs can reduce a weak battery's Voltage to the starter enough to prevent the engine from spinning fast enough to start as you expect. The starter can deteriorate too, by having the insulation break down on the windings, with a similar effect - slower than normal turning leading to difficulty starting.

Since the engine runs on the principle of heat generated by the compression of the air achieving a temperature that is great enough to ignite the Diesel fuel when it is injected, anything that lowers this temperature can adversely affect running and especially starting. Slow turning of the engine gives the heat generated by compression time to get absorbed by the block and head (usually cold at start up). Consequently the engine will not start right away. A few seconds of cranking and the immediate area around the combustion chamber is warmed up enough so there is sufficient heat to support ignition.

Glow plug issues are usually accompanied by odd behaviour of the glow plug light on the dash. Like it won't light up the first time you twist the key to the normal glow plug lighting position, or it blinks or some other event. You did not report any glow plug anomolies so I am presuming the glow plugs are ok.

So, I would check the battery Voltage before you start, while the glow plugs are on , while it is cranking the starter and after it is running. In general, the battery should be over 12.5 Volts just sitting there, and, with the engine running the system Voltage should be at 13.6 or slightly higher. If you are not within these ranges, either the battery or the charging system is at fault. If the battery and charging system are ok, I would suspect the starter. You can take it out and have it checked, but if it is weak, I would get a rebuilt one from FastLane. Diesels are hard on the starter and battery.

Good luck, and I hope this helps. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)