My 2004 Holden Astra is leaking engine oil from around the rocker cover

This engine has a reputation for failed EGR valves which are part of the emissions control system and live within the rocker cover. Without this valve working properly, the car’s tailpipe emissions can be higher than they should be, as well as causing the oil leak you’ve noted. And any time you have oil hitting a hot exhaust system, there’s the potential for a fire.

In some cases you can simply change the EGR valve, but experience suggests that with some engines, the solution is to replace the entire rocker cover which will incorporate a new EGR valve. The parts can usually be bought online.