To ensure that your final drives are leaking oil, please check the following:

NOTE: A small amount of oil vapour (weeping oil) around the gasket and bolts is normal. 

Check to see if the gasket is mounted securely and is not torn or damaged. 

If there are visible drops of oil then check the torque of the bolts  (9 Nm) mounting the final drive cover plate. 

If they are all secure then you will need to replace the gasket.