I never made a post about this but my Wife's 170 has had an exhaust fumes smell since we got it over a year ago.
I did various searches on here and other forums and got loads of ideas what it might be. We were fairly sure it was exhaust fumes and it was coming though the heater but checking under the bonnet came up with nothing in particular that could be causing it. I had the under tray off and the exhaust and all pipes seemed fine, tried semi blocking the tail pipes to see if anything would come out towards the front but nothing.
I read that the underside of the bonnet needed to seal to the bulkhead/inner wings, cleanerdall the seals,no rips of tears etc, changed the pollen filter, nothing.
She was at the point of being so sick of it she was taking about trading it in, then I was on her doing my usual luinchtime browse at work and I was looking at pictures of Jardo's new A3 TDI, when suddenly it hit me, he has a seal all the way round the inner wings and our's stopped about 10 inches short at each side. I checked some other pictures and another car and sure enough our seal was short (WHY would anyone cut it or is it the wrong seal, probably never know?) anyway I got a bit of seal from a scrappies (Passat seems the same) and jointed it in - NO fumes
Will buy a new seal now as it's obviously worth it, can't completely give Jardo credit but cheers mate anyway