The brief
The X4 had oil leaks, a burning oil smell, the odd misfire, a touch of smoke from the exhaust, and oil found around the spark plugs. He brought it in before it cost a coil or worse. The valve cover sits on top of the engine and seals the camshafts and valvetrain in. On these it is a plastic cover, and over years of heat the plastic warps and the gasket hardens, so oil starts weeping out along the seam. That is the leaks and the burning smell when it drips onto something hot. If it tracks into a plug well it soaks the coil boot, which is the misfires and the smoke. A warped valve cover only gets worse, and an engine running on oil-fouled plugs runs poorly, so it needs the cover changed.
The diagnosis
On the lift the leak was confirmed at the valve cover. The plastic had warped enough that the gasket couldn't seal along part of the seam, and oil had been weeping down the side of the engine and into a plug well. The other gaskets in the area were dry. That's a valve cover replacement, not just a re-gasket. A warped plastic cover won't seal reliably no matter how good the new gasket is, so the cover and its gasket both get changed, and the oily plug well cleaned out while it's open.
The work
The ignition coils and the old valve cover came off, the camshaft area and the oil-soaked plug well were cleaned up, and a new genuine BMW-spec valve cover went on with a fresh gasket, the bolts torqued to spec in the proper pattern. The coil boots were cleaned and everything reseated, and the stored fault codes cleared. Then the engine was run to confirm it was firing cleanly with no leak, followed by a road test.
The outcome
Dry valve cover, a clean bay liner after the road test, no burning smell, no misfires or smoke, and the engine running smooth with no fault codes. The X4 went home with the top of the engine sealed properly. An oil leak at the valve cover only spreads, and once it's into the plug wells it starts costing coils, so sorting the cover when it did kept the job to the cover and a clean-up.
