[spannerrash]

As Mark has already said, the Valley cover gasket is a worthwhile fix if you can remove or get a mechanic to remove the manifold for you. Mine was leaking quite badly. There is a hole in the rear of the block, under the manifold, that lets the oil run down the back of the engine if it builds up too high. You could also do (or get done) the oil retention valves whilst in there. They're not really problematic but cheap enough to replace whilst in there. Just be careful removing them, they can be quite tight.

I would source a scan tool if I were you to see if the knock sensor is faulty. Pinking or pinging, I'm not sure which one it is, has a number of possible causes with the knock sensor probably being the easiest thing to check.

Just be careful. Pre-ignition can lead to further engine damage if severe and persistent enough. I do not wish to scare you but personally I would limit how much I drive the car until sorted.