Yes, I had the o-ring fail at the alternator. Is replacing it difficult. Depends how comfortable you are in removing the throttle bodies. Not hard but time consuming.
I was unable to determine that it was in fact the o-ring, until I actually removed it. The alternator that is. Even with a bore scope you could not see where my oil was coming from and it was causing a small stream running out of the square hole when the engine was running.
Based on my situation, the mechanic is "good" if he can tell it is only a drop a day.
Are you seeing oil or any kind of seepage from the square hole or on the ground on the right front side of the engine?
It could be coolant mixed with grime that he/you are also seeing from loose coolant clamps in the "V".
I would start there, tightening up the clamps.
Kevin