Checking turbo seal leak

[ixReaperrr]

I recently got my Polo 1.6 TDI 75bhp remapped and dpf delete. After getting it dyno'd it was only pushing 105bhp rather than 140 and the tuner has said this is due to the turbo seal leaking. What would be the best way to confirm whether the turbo seal is leaking or there is just a bad map on the car. The car runs without any white smoke and there is no whirring noises.

[iichel]

You'd probably see some soot residue where the exhaust manifold meets the engine block.

[Vwpolotsi]

Hi
I own vw polo tsi 1.2 2011 .. my issue is sometimes i saw greasy on my turbo..anyone can advise me on this. Tq

Picture as attached. Thanks