Use a pair of water pump pliers with a rag wrapped round it to prevent damaging the plastic on the cap it definitely works reason why its so tight is because it has not been removed for such a long time the rubber seal on the cap bonds onto the metal of the can cover either the previous owner has never had to top up with oil or just not checked the oil level.I believe its the former as most Jazz's do not need topping up of oil in between services!!