I noticed some sparks and smoke coming from the wire connecting the starter to the solenoid after cranking for about 5-8 seconds. The wire was hot. I figured it's a bad connection at the solenoid and went to remove the wire to try to repair it (solder). I put the 13mm socket on it and started loosening. But the nut stays put and the threads/stud spin! Though it seem like there should be, there is no bolt head to hold on the back of the solenoid.

Since the stud appears to just spin in the solenoid, I guessing that means something inside the just solenoid broke. Does that mean my entire starter is toast all just for a bad wire and now stud on the solenoid?

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1986 300 SDL, gray on black, #14 head, 180K miles
1982 300 CD, silver on palomino, 290K+ miles [sold]
1980 300 SD, white on palomino, 500K+ miles when retired [uncle's car - inspiration for the above]