When removing the top plastic engine cover, i noticed that the cover had been rubbing on the cam cover, the aluminum cover is getting very thin in this area. To stop it wearing anymore I've suck self adhesive spacers to the clips that hold the cover in place. This has raised the cover and it does not rub anymore. This may be worth checking if you have a similar vehicle. The place it was rubbing was on the top of the right hand side cam cover behind the oil filler.