Oh, one other thing about boost leaks - they can be easy to spot as there often a lot of oil vapour in the boost air which leave an oily stain around the leak. Check for oily stains on entire high pressure air system...
image from osiris at bmwfanatics.co.za
The charge air temp sensor on the intercooler outlet pipe can fail to seal sometimes - I know mine needs sealing up (from the oily state of it...).