battery acid, coolant weeping, or normal surface oxidation depending on where you live

 

You are correct, but believe it or not, I had an exhaust leak at the turbo and was seeing white ash on top of the intake manifold.
Most of the time you will see a black carbon soot right where the leak is, (ask me how I know ) but I think there is also a white-ish ash flakes that float around ....
I am guessing once he plugs that leak at the test pipe we will finally know
Best regards
Ed

 

I had a similar white residue all around the engine bay. It was from between the intercooler fins. The intercooler had been sat idle for a number of years...

 

Just had another go at this...it still won't budge. It turned out I hadn't re-tightened the nut from my last attempt, so I've been driving with it loose for a while. Today I sprayed it with penetrating fluid and spent half an hour trying to get it loose...even went for a drive and got the car nice and hot. That thing is seriously stuck in there.