Long story short my lad has been given a 2004 1.6 TDCi C-Max to learn in and it has a boost leak, wooshing noise at 2000 rpm and over.  I have cleaned the engine bay down as it was in a mess and the oily mist is coming back by a concertina plastic pipe that connects to the inlet manifold.  It appears to be spraying down onto the exhaust manifold and rocker cover area (see picture below).

I have taken the pipe off and for the life of me I can't see a split.  Is there a common failure point in this area that I may be overlooking?  Any advice would be much appreciated.

A "whooshing" noise is a sure sign of a leak at turbo or intercooler

Sometimes these leaks in pipes can be B*@&%"+*ds to locate/find only opening up when under pressure (in your case at 2000+ rpm)

As you have found 'misting' that would suggest a pinhole causing the oil to spray so it may be very small indeed even under pressure

Sounds like that concertina pipe needs replacing unless the securing clips are faulty 

Sometimes it is the simplest things you just don't think of.  I was trying to think of ways to pressurise the pipe etc and my misses taped a plastic bag around the pipe and told me to take it for a drive.  15 minutes later we un-taped the bag and there was oil inside.  Pipe is dead and I am shamed by my good lady.

I feel a bit silly I didn't think of the obvious but hopefully it helps someone else. 🙄🙄🙄

Diagnostic TIP of the day 

Great tip