diesel fumes inside cabin

[Maggiemoo]

Had exactly the same issue, it was the exhaust gasket at the back of the engine between the turbo and DPF filter at fault. To test it, when cold spray some fairy liquid/water around the V-Clamp, you will see it bubbling away.

I did the job myself twice, first time used a cheap gasket which didn't work so id advise to obtain gasket from VW.

You need raise the car on a set of ramps and remove DPF supporting nuts at the back of the engine to allow the DPF to move for access, disconnect the V band clamp, move the DPF out of the way, remove and replace the gasket.

[Jon44w]

The exhaust joining section clamps also corrode and fall off. This allows fumes into the cabin. Potentially lethal.