We were three-quarters of the way through treating this MG with Renovo Ultra Proofer, when there was a sudden summer down-pour. Can you tell which quarter of the roof we hadn't done yet?

For a number of weeks after Renovo is applied, it will be so water repellant that it will cause rain to bead up and roll off. This effect will gradually fade (This happens until the hood starts absorbing dirt and dust which will break the surface tension), but this does not mean that your hood is no longer protected. You can tell if your hood is protected because after rain, it will be damp to the touch. If the protection has worn off, it will be sopping wet. You can see from the top photo that the quarter that hasn't been treated is soaked through. Imagine if there was now a heavy frost and the wear that would cause to your hood!