I haven't had a full built (non-Zytel) Arc-lock yet, but both my Pentagon and Pentagon II developed vertical play. My advice is, send it to SOG and tell them it needs warranty work, and next time, buy a Benchmade or Spyderco - the Ball Lock is the only Axis clone that's up to snuff, neither SOG nor Cold Steel do it well enough, in my experience.
I like SOG fixed blades and lockbacks just fine.