Just completed 6,000 miles since my last oil change. The car had a "B" service 10 January 2001 at 38,232 miles. It is now 27 March and it has done 44,200. I know the secret to longevity is to change the oil at 3,000 mile intervals, but that would mean every 5 weeks for me!

The ASSYST service interval indicator suggests I will need a service in 5,000 miles. However, I checked the oil level at the weekend and it was starting to look a little dark in colour (although no oil consumption at all since the last change).

I'll probably keep the car for a couple of years at least, maybe more. Should I have an oil change service?

If so, should I change to a fully synthetic oil. My father always uses Mobil 1. At present the car contains Mobil S. I have heard that unless a car has run on synthetic all its life, you should not use synthetic oil as the oil seals will shrink slightly and some minor oil leaks will develop. Is this so? Should I run with some kind of oil flush product for a few hundred miles before the change? Should I change to semi-synthetic first before moving on to a fully synthetic oil, thus making the change gradual?

I know this is an old chestnut...