I have no clue what is also going on. But if I am reading right I want to make sure you do not have any part of the bolt in place. Some joints have a safety feature where a grove is tapered in where the bolt passes by. This is in the case of the bolt becoming loose, with the groove the ball joint can not come out unless the bolt falls all the way out. If the bolt is there when inserting, it will not insert.

Wild guess here.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car