Metal slimes flee cuz ur level is too high. Go to Bowhole B3. Wait a minute and ull see Liquid metal slimes. Theyre not fleeing so much and they give 40000 EXP.
yer guess fleeing is a problem but you could always try metal medlys. use metal slash on them and you should be able to kill them in a couple of turns (at the same point in the game as you though just beat the empire)
Try using moves that hit multiple times when attacking LMS or use critical hit moves like Thunder Thrust and Hatchet Man. Criticals will kill them in one hit.
ok, i still think your warriors metal slash is the way to go. What levels are you and your team members? You might not need to train your team up at all+ only three of you?