Engine oil sludge does not just affect Saabs, take at look at the oil pan and lower engine on this VW Passat. That black gooey substance is not tar, but engine oil sludge. Unfortunately the car was switched over to a full synthetic engine oil too late in its life, for the first three years it was run on a conventional oil, you can see the results. It is cheap insurance to always use a fully synthetic engine oil on all European autos newer than 1999. We use Castrol Syntec in our workshop, it is the factory fill on many of the European imports.