It's been a while since I looked at one but I think there should be a nut holding the transmission end of the flex disc mount on the transmission output shaft. But if it's pulling out of the transmission, I think it also means that the big nut in the middle of the driveshaft must be loose allowing it to shorten up enough to allow the front of the driveshaft to move back.

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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