Blue smoke is oil, not fuel. Its rare for one of these engines to pump out blue smoke as valve seals last a VERY long time. Heads are a problem on this car, the original design was weak and MB redesigned a few times before they got it right. Head gaskets too. However, its almost always both. The head can crack here and there and the engine will run fine, but exhibit some odd behavior. For example, it may maintain cooling system pressure for weeks if not driven (overnight it should zero out). Test by pinching the upper radiator hose in the morning before you start it. IF its tight as a banjo string... A cracked head or bad head gasket can also be a source of low compression most noticably when you are starting the car. Head replacement is about $2000+ if you do the work yourself. Reputable shops do not sell used heads because originals were known for problems.

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Brian Toscano