error code p2457 on e70 diesel

[scorpioy]

My car is 2009 e70 diesel. I noticed since early this year, the EGR started some kind of leaking in the middle of the tube at a joint. Till now, it's kind of a layer of black soot around the tube. See attached picture.

It was until yesterday, at 101,500 km, the car showed up first time for the check engine light. I used my own OBD reader and found 2 errors: $7E8 and $7EC. My reader can't identify $7EC. For $7E8, it's code is p2457, which is exhaust gas recirculation cooling system performance.

I googled this p2457, and only a few people talking about this in e90. So it seems this does not happen often yet in X5. Maybe just me having bad luck on this leaking EGR? Do I have to replace the entire EGR unit?

Thanks