Now that everything is dry and securely welded make sure you can unscrew the threaded bolt end from the rest of the nut assembly. If you were careful you shouldn't have to worry too much.
Place the log inside, re attach the top of the geocache and find something outside that has a lot of nuts and bolts holding it together (like a water pipe assembly in a park or a metal gate).
Separate the two halves of the geocache and arrange them as if it were actually a bolt penetrating something metal.
Log the coordinates on a geocaching website and watch as the "didn't find it" responses grow and grow.