The brief
Mr Kelvin's 535i came in with an engine oil leak, spots on the driveway and oil cooking off under the bonnet. He brought it in to get it sealed before the level dropped far enough to be an engine problem. The oil sump is the pan that holds the engine's oil, bolted to the bottom of the block and sealed against it with a gasket. Over the years that gasket hardens, loses its squeeze, and lets oil weep out around the join, which runs down and drips. A hardened sump gasket doesn't reseal, so the sump has to come off and a fresh gasket go in.
The diagnosis
On the lift the leak traced to the oil sump, the gasket weeping where the sump bolts to the block, which is the drips. The rest of the engine, the valve cover, the filter housing, the crank seals, was dry. That's an oil sump gasket replacement, the sump off and a fresh gasket in with the area cleaned up, rather than chasing a weep that only spreads.
The work
The metal oil sump cover was unbolted and removed, the old hardened gasket taken off and the mating faces cleaned, and as a matter of habit the sump cover was washed clean while it was off. A new genuine BMW-spec sump gasket was fitted, the sump torqued back down to the manual figures, the oil level checked and topped, and the area cleaned of old oil so any future weep shows up. A road test and a check on the lift confirmed the engine dry, no drips, and the level holding.
The outcome
No oil leak, the engine dry, no drips on the driveway, no oil burning off under the bonnet, and the level holding between checks. Mr Kelvin got the 535i back sealed up, sorted quickly. A hardened sump gasket only weeps more the longer it runs, so replacing it and cleaning up the area fixed the leak properly and made the next inspection straightforward.
