What codes did they pull? It should lead them to the problem, diagnostics run four pages, I have the engine manual on that car, I would be happy to look up the codes for you, on the other hand if you need a pump call either CALIBERE or Fletcher Jones they will give wholesale pricing on a BOSCH rebuild, I have heard mixed reviews about Gus at Pacific Injection, also if you send yours out to be rebuilt send your injectors out to be tested, try to have them calibrated to within 5 bar, 10 bar is spec makes a noticable difference. Good luck
Ron
1985 300TDT
1993 300 D
1998 E300 sold
1999 E320 AWD WAGON
2003 E55 AMG
2004 E320 CDI on order