Was there any evidence of any substance in the tank? If there was nothing in the filters, then it's hard to understand what would have damaged the IP. Does anyone know what sugar does when dissolved in diesel fuel? Could it pass thru the filters and damage the IP?
Did the mechanic try running it on an alternative fuel supply as I described?
What primer pump does it have? The old white screw tight kind or the newer spring loaded one? Did you or the mechanic use the primer pump during the testing process? Could it be letting air into the system? Could air be getting in some other way after working on the system?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13