Although the return line o-ring is a common item, one will usually see "normal seapage" from what APPEARS to the the bottom of the turbo itself BUT the oil seen there is the result of seapage from the air intake tube from where it's clamped at the turbo. That tube's the large one from the MAF meter and what I do is just tighten that clamp at the turbo, degrease the turbo and if still in doubt, drive the car and make sure it's not leaking from another source.
It's NEVER the result of a "bad turbo". There is always some oil mist normally in the intercooler hoses on all turbo cars so it's not unusual to see a little seapage from where that hose connects and at the bottom of the intercooler as well, not a problem.