I’m having a problem with the boolean operations. On Union I get scattered bits of mesh (presumably problem areas), on Difference I get the same thing and also the other object with flipped normals, and on Intersect it combines them to one object, but not the meshes (2 loose parts). Screenshots along with a blend file can be seen here:
You might want to check the mesh normals, the reason for that is that inconsistent normals and non-manifold surfaces would be a key reason as for why operations like boolean would fail.
Go into edit mode, select all, and do ‘recalculate normals’, if that doesn’t help, go into edge mode and choose ‘non manifold’ in the select menu to see if you get anything.
Also check for overlapping faces or large pieces of geometry that clip through another area, as that could happen if you’re not careful when sculpting.