1. Find an independent, your dealer is ripping you off.
2. You say oil is leaking "again", did you already have an oil leak repaired? The valley pan leak you mention would have resulted in coolant (green fluid) leaking along the back of the manifold and down the bell housing, not oil (common on 4.4)
3. Why did they say you need new O2 sensors, is it throwing a code?
4. see #1 above .............