My girlfriend has an EL fairmont (1997?) converted to manual, she's bought recently with a touch over 300,000km on it, and showing a little age. Running down the gold coast everyday she's doing 6-700km+ per week. Changing engine, diff and gearbox oils and using PM800 immediately I don't have before/ after figures but she religiously gets 680km per tank or a couple of km more with a few litres left 'just incase'. She's too slack to fill her own bottle of PM800 up, so if she doesn't tell me it doesn't get done. So on the second tank without PM800 she bled it dry, dropped 110km and filling up a day early. She's not happy.
She now knows to make sure she tells me when she needs more ;)