I'd get a second opinion - preferrably at a Volvo certified repair facility that has access to a Volvo OBD scanner. I mean it's totally possible for all these items to be faulty but it's rather unlikely for them to all go together all at once. The front O2 sensor could be bad but $380 is a bit on the high side even if you go with the Volvo branded O2 sensor. The oil leak can be a costly repair if it's the sump pan that is leaking but if the leak isn't causing you to add a lot of oil on a regular basis then just leave it alone. But the most likely cause for your oil leak is the turbo oil return line. This is a cheap fix and only requires a new O-ring to be replaced.

Good luck.