There is a bit of leakage under part throttle at cruising speeds (60mph). Is this normal or is the BOV springs too weak? BTW car is stock.

 

Stock BOV has a good spring on it. Really, you might be hearing the second turbo pre-spooling - the charge relief vents the boost from the second turbo back into the airbox below 4500 RPM.

Unless you have actual boost problems, I doubt there's anything wrong. A leaky BOV would show up as reduced boost patterns.

Dale

 

People have noted that after venting the stock BOV, it does blow a little air while not on boost. However, it should stop once you begin to build boost.

 

If you have a vented BOV, its perfectly normal.