It's very common for the turbo return line seal to leak oil. When they leak it can be minor seepage that may be hardly noticeable to a very large oil leak that can cover the entire underside of the vehicle. The part is very inexpensive but the job takes at least an hour due to the AWD differential that is in the way.Google+
Car Problem Reports
Volvo XC70 Oil leaking from the engine, dripping off the oil pan.
Volvo XC70 Problem
Visitor, 2003 Volvo XC70, 130,000 mi
Small oil leak spoteed near turbo by oil change place. Took to local shop and they said oil line O rings need replacement. They will replace the feed line that includes new O rings.