As a classic owner, do you of course tinker yourself? Therefore, the valve cover must be regularly disassembled to adjust the valves. And then you suddenly see that the inside of the valve cover is provided with a tasty (...) white slurry that reminds you of mayonnaise ... 'Sludgeis called that in technical language. No panic, that does not necessarily mean that the head gasket (from a water-cooled engine) has left, that a crack has occurred in the cylinder head or that 'water' is added to the oil in some other way. This is because a mixture of condensation and engine oil was created because the machine is used for short journeys or the oil is not regularly changed, the engine does not get sufficiently 'warm'. From now on you will therefore have to make longer journeys and change oil more often. Perhaps it is good to know that an engine is not running 'warm' as soon as the temperature meter indicates 'N' (from 'Normal') or 80 degrees ... That 'warm' running often takes more than an hour. The problem can be solved quickly. Thoroughly clean the valve cover (inside), adjust the valves, change the oil and oil filter and then make a long drive, bringing the whole to the operating temperature… sludge can also occur with an air-cooled engine ... Has the same cause and can be remedied in the same way!