My petrol focus has covered 189,000 miles and as now started to use a lot of oil, there are NO leaks. It has been to the garage and had the rocker cover seal replaced. They reported no other problems.

The car is very reliable, I often do runs of 500 miles, getting >38mpg. The only thing I need to do is fill up with oil.

Any ideas please

At that mileage oil consumption is likely to get high, its a simple fact. Keep filling it with oil but do not buy any of the wonder products they sell on E-Bay and Halfords etc, will only cause problems.

If you want to keep the car long term get another engine from a write off, plenty out there.