I guess you had to collapse the driveshaft to get the flex discs out? To do so, you probably loosened the big (48mm?) nut in the middle of the shaft where the front and rear halves meet.
The manual calls for 30-40Nm when re-tightening this nut. That is very little considering the size of the nut. Actually, this is on purpose as the driveshaft needs to adjust slightly in length to relieve stress. When the nut is too tight, stress may cause vibrations.
Bruno

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1992 300TE 160 kmiles