Greetings, I bought used manual W202 C200 Elegance from 1995 and I am happy with the performance and comfort of the car(had E36 before).I inspected everything on the car and it is in very good shape but one thing bothers me.Upon opening the expansion tank cap,it had mayo on it,and the water was all brown with some sludge in it.I scrapped the walls of the tank with my finger and there was more of that brown sludge and mayo.Upon researching,I found it it can be a blown head gasket,but my car doesn't have all the regular symptoms. It starts up with no hiccup,either hot or cold,there is no mayo under the oil cap,it doesn't smoke,only when it is a bit colder outside,it has plenty of gas,and it idles smoothly(it also has LPG,it idles a bit rougher on it but still not very noticable),and the most important thing-cooling system is not pressurized.When I open the cap,either warm or cold,there isn't even a slight hiss.