Brainiac 5 - Brainy doesn't have to get close to figure out a way to stop Amazo, as long as he has...
M'Onel - Mon can attack Amazo from afar, and is fast enough to *just* keep out of range, plus his vision powers can give Brainy all the data he needs about Amazo's insides. And he can keep Amazo busy long enough for Brainy to work.
Chuck Taine - okay, he's definitely not in Brainy's IQ league, but Chuck does have the mechanical expertise, and two heads are better than one. I picked him over Gear because Gear will probably have his hands full keeping Legion World from getting damaged.
Lady Mysa - Amazo already has magical abilties anyway, so Mysa can feel free to step in and help slow him down any way she knows how
Kinetix - Amazo may be a technological marvel, but he's still made up of matter - and Kinetix is the best matter manipulator left in the Legion after Element Lad.
Shikari - not only could she find Amazo if the need arose, but she could also "see" his path before he takes it - which should help Brainy make a foolproof plan for taking Amazo down.
Next: The Time Trapper has caused the Legion's 30th century to start merging with the real world! Which six Legionnaires would get shunted to our present, and what would they do while waiting for their teammates to fix the temporal madness?