I would get another opinion, sounds to me like a fuel starvation problem (like a clogged filter) if you actually do have a problem. I've never heard anything like that about an injection pump, especially not on a MB. Unless you're noticing a problem I actually wouldn't mess with it.

On edit, how many miles does it have on it? That will give us an idea if it actually could be worn out.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k