mate do it wile its out ,this is the big downfall of the essex and they are not to expesive to buy and its piece of mind! so easy just drop the oil and drop the sump this way you can cleen the sump as well and take the pump out you will see hoe it works ,but make shure you get it back in proply and not up the side of the dizzy its easy to do! when you re start it ,make shure it has preshure then you know its in proply