I just soloed this as a 60 affliction lock in substandard gear.  I cheated a bit as I cleared the cave with my 70.  I say cheated because there was one pull behind him which may have been hard to get at level.

No secrets here.  Hit a couple of your instacast dots, and then fear.  Stick your long ones on him and then rinse and repeat.  I drained my imp a couple of times and life tapped once.  I think in the whole 2 minute 50 second fight he touched me three times, and that's when the fear was resisted.  Never touched any potions, my healthstone or soulstone.