Did you test it while out of the car to make sure the bendix is coming out? Using jumper cables to the battery to test it. If the bendix was coming out while out of the car, I'd look at the flywheel. But my guess is that the bendix is sticking for some reason.

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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