Oil leakage under carriage. Can't seem to find where it's coming from.

How are you cleaning the under carriage? Best way would be to get it steam cleaned, then leave the car running while it's raised to check for leaks. Could be coming from anywhere. May not even be oil!

Suggest using uv sensitive dye added to suspected leaking fluid (Google for more information) .. The color of fluid that's leaking should be a clue .. plus the fill level of leaking fluid should show a deficit when checked.