The brief
The C180 had a burning smell coming off the engine bay, that unmistakable scent of engine oil cooking on something hot, especially after a run. He brought it in. On these engines that smell usually points at the valve cover gasket. The valve cover sits on top of the cylinder head and seals the top of the engine, keeping the oil in, with a gasket between it and the head. Over years of heat cycling the gasket hardens, shrinks and cracks, so the seal lets go and oil seeps out the edge. It runs down onto the exhaust manifold or other hot parts and burns off, which is the smell, and if it's left it can drip onto things it shouldn't and the oil loss adds up. A hardened gasket doesn't reseal, so it needs replacing.
The diagnosis
A check with the engine warm found it, oil weeping from the valve cover gasket, running down onto hot parts where it was burning off and making the smell. The rest of the engine's seals, the oil filter housing, the sump, the crank seals, checked out dry, so it was the valve cover gasket. That's a gasket replacement, and on these the valve cover is plastic, so it gets inspected for warping while it's off, but the gasket is the fix.
The work
The intake and the bits in the way came off, the valve cover removed, the cover and the head face cleaned up properly, the cover checked over, and a new genuine Mercedes-spec valve cover gasket fitted, every bolt torqued in sequence to spec so it seats evenly. The oil was topped to level and the engine run and checked warm for any weep. A road test confirmed the burning smell was gone and the cover was dry.
The outcome
No more burning oil smell, the valve cover sealed and dry, and the oil staying where it should. The C180 went home with the leak sorted. A hardened valve cover gasket only seeps worse and keeps cooking oil onto hot parts, so changing the gasket stopped the leak at its source, a clean engine and no more smell.
