I recently discovered that my rear diff was leaking too. after I cleaned up the mess, I realised MMS didnt do up my diff oil plugs tight enough when I went in for a service. I tightened up the bottom plug and topped it up a bit from the top plug and all was good.

The only possibility is the diff rear plate gasket is leaking. Which would mean you rear diff needs to come out in order to replace that. But its not a big task for a mechanic.

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RS Liberty - Because WRX's are only good for parts...