The brief
The 318i had been leaving oil stains where it parked, the kind that build up over time, with the oil level dropping, a burning oil smell after drives, and residue around the bottom of the engine. He brought it in before the level got away from him. Oil stains under the car and a level that keeps dropping point at a leak, and the sump is a common source. The sump is the pan that holds the engine's oil supply, bolted to the bottom of the block on a gasket. Over years of heat that gasket hardens and stops sealing along the seam, so oil weeps out and drips, and some of it lands on hot exhaust parts, which is the burning smell. It's a slow loss, but an engine that runs low on oil is one you don't want to keep driving, so it needs resealing rather than topping up.
The diagnosis
On the lift the leak traced cleanly to the sump gasket, weeping along the seam, with the other seals around it, the timing cover, the rear main, dry. The gasket had hardened past sealing, the typical age-related failure. That's a gasket replacement, drop the sump and reseal it. The pan itself and the bolt seats were fine, so it was a fresh gasket.
The work
The engine oil was drained, the engine supported, and the sump dropped. Both mating surfaces were cleaned back to bare metal, a new genuine BMW-spec sump gasket fitted, the bolts torqued in the right pattern, and the engine refilled with fresh oil to the correct spec. Then it was held at idle and checked underneath to confirm the new seal was dry. A road test followed to confirm it stayed dry and the level held.
The outcome
Dry sump, dry seam, no stains under the car, the oil level holding, and no burning smell. The 318i went home with the leak closed off and a clean underside. A sump 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.
