I had this problem for ages it drove me nuts!!!! My smoke pressure tests didn't loose any pressure though! You checked your dv? Checked all the pipes are firmly in properly? Mine was caused by my gasket on my downpipe from the turbo!
Did you replace the gasket on the inlet manifold? Only others I could think of are:-air intake pipe to turbo- DV split-intercooler pipes - PCV where it connects to inlet mani (or boost gauge tap if you have one)
Yeah that's the one! Replaced it and it never came back! It fell apart in my hands :/ Strange I know, only noticed it was gone when trying to look for the leak!