It may sound silly, but first I would smell it to decide if it was engine oil or gearbox oil.
Gearbox oil is usually thicker and with a stronger smell than engine oil. If gear oil it would involve the front oil seal in the gearbox and maybe the first motion shaft bearing if a lot of movment there.
I suspect it is engine oil and in the absence of oil leaks higher than the top of gearbox bell housing I would suspect it was coming from the rear main bearing oil seal behind the flywheel.
If that is the case it involves gearbox or engine removal to access behind flywheel etc.
Did you post another thread recently saying you had only just bought the vehicle? If that is the case you may want to speak to the seller as this hasn't just happened!