Plugs on a 172 are supposed to be good for 72k , i think thats a bit optimistic , mine lasted about 30k . You can buy the cover that covers the oil filler cap separate from Renault .The clips do tend to break off easily , best thing to do whenchanging your oil or if somebody else is going to change the oil is remove the whole engine cover first then you / they won't snap the clip off . You shouldn't need to change the leads unless you have a problem .