G2RSR is right.
Alot of people seem to think that you should look to use a thicker oil with a car this old but they're wrong. Ask any oil manufacturer and they'll tell you that 5/50 is what you should be using.
Millers is a good oil, have a look on this site for future reference Passionford members get discount.
http://www.opieoils.co.uk/p-60214-mi...ngine-oil.aspx
Big-Dan.