I have just added to my web site a new service. I am waiting for kits and bottles to arrive.
You can send me oil samples either from your car or a car you are looking to buy.
The oil samples will give a good indication as to the health of your engine.
Oil has trace eliments in it from all the working parts of your engine, just like a doctor would test your blood.
http://www.hannibalrx7.co.uk/acatalog/Royal_Purple_Oils.html