The brief
The B180 had been leaving oil puddles where it parked, with a burning oil smell while driving and after parking, visible oil dripping and pooling on the engine, and the level dropping enough to need topping up. He brought it in. Those symptoms point at an oil leak from the engine, and on these the oil filter housing is a common source. The oil filter sits in a housing on the engine, sealed with a gasket that the engine oil flows past, and over years of heat that gasket hardens and stops sealing, so oil weeps out, which is the puddles, the wetness on the engine and the burning smell when it drips onto something hot. Left long enough, a low oil level affects the engine's running, so it needs the gasket changed rather than topping up.
The diagnosis
On the lift the leak traced cleanly to the oil filter housing gasket, weeping along the seam where it bolts to the engine, with the valve cover and the other seals dry. The gasket had hardened past sealing. That's a gasket replacement, take the housing off and reseal it. The housing itself was fine, so it was a fresh gasket.
The work
The oil filter housing was unbolted, the old gasket removed, and the mating faces cleaned back to bare metal. A new genuine Mercedes-spec gasket went on, the housing torqued back up to spec, the oil that had tracked down cleaned off, and the engine topped to the correct level with the right spec oil. Then it was held at idle and checked to confirm the new seal was dry. A road test followed to confirm it stayed dry and the level held.
The outcome
Dry housing, no puddles under the car, the oil level holding, no burning smell, and the engine bay clean. The B180 went home with the leak closed off. An oil filter housing gasket leak only spreads, and once it's letting the level drop the engine pays for it, so resealing it kept the job to a tidy one.