Mercedes did face reliability issue (electricals switched off) in Canada, there is no way they are going to reveal what exactly it is, to Mclaren (even though 2-3 engineers from HPP Brixworth are 'loaned' to McLaren, they won't be told the root cause of the problems, because the engine buying contract doesn't make it mandatory, as per my understanding). So McLaren will need to 'peel the onion' which Mercedes already did.