Stalling automatic

Hey all. I have a friend with an auto V6 2005 Toyota Mk X that keeps randomly stalling and sometimes not starting. So far 3 mechanics have failed to find the cause. He is thinking it may be a leak in the high pressure fuel pump that sits at the back of the engine because it has a white chalk-like powder coating it and the surrounding area (Can anyone ID what the powder might be?). Im wondering if anyone here may have an idea for what may be the cause of the stalling?

So far the starter motor has been replaced and didnt fix the issue, low pressure fuel pump by the fual tank has been checked and was ok, and the throttle body has been cleaned which gave it heaps more power when the car works but didnt fix the stalling.