I glue them by holding the head and antenna together and squirting a bit of acetone with a thin syringe needle, it seeps into the gap and if I miss it won't deform other feature as it's just a solvent without the plastic in it. I do this multiple times, it evaporates quickly from surface but not from the gap, giving it time to "melt" it at the correct spot.
The two contact surface shall be plain, add a little bit of super attack and wait 20 seconds. Pay attention on the quantity of glue. Too much glue flowes over the connection of the two bits and creates roughtness. You have to understand the right quantity!