I see two possibilities.
The oil leak has caused the clutch to slip. I saw this once on an old '50s Jaguar. The Jag looked like my Dad's 2.4 L but this one was a 3 point something. A bad gasket caused oil to slowly leak on the clutch. A temporary "fix" was to engage the clutch with the engine revved up so as to burn off the oil. What the heck! The clutch was toast anyway.
However, I think your problem occurred suddenly, so instead of a bad clutch, you have a broken drive link somewhere. This broken link, whatever it is, is now a piece of metal free to move around inside the drive train, has interfered with the motion of another part, and has punched a hole in either the transmission gear case or the engine block, creating an oil leak. It sounds awfully expensive.