I suspect you are on the correct trail with the leaking primer pump -- air gets drawn into the fuel system when the pump leaks. This can result in hard starts, although usually cold starts are bad, too.

Check the starter motor for current draw and for proper engine RPM -- engine must turn at least 100 rpm or it will not start, period.

My volvo does the same thing -- immediate restarts are fine, but if it has been sitting for a while (15 minutes or so), the glow plugs don't appear to run (no dash light), and I have to crank for a while to get it lit. Rattles then goes fine, with a blast of white smoke. Has 215, 000 plus miles with no evidence of starter replacement, so I cannot complain!

Otherwise, check the fuel system -- clogs, plugs, leaking lines, and a plugged restrictor or pressure valve in the fuel filter or the retrun line from the IP can all cause hot start problems from improper fuel delivery.

So can iffy glow plugs, buy the way -- how old are yours? If they are three or four years old, they may be heating slowly, and not getting hot enough when the engine is warm!

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!