The brief
Mr Tan had been living with an engine oil leak on his Audi for a while before he brought it in for a look. An oil leak that's left alone means topping up between services, spots on the driveway, and oil cooking onto hot parts under the bonnet, and if the level ever drops far enough it's an engine problem, so it's worth sealing properly. A common oil leak on these is the oil filter housing gasket. The oil filter housing bolts to the engine block and seals against it with a gasket, and that gasket sits in heat and oil for years until it hardens and loses its squeeze, so oil weeps out around the housing and runs down the block. A hardened gasket doesn't reseal, so it needs replacing.
The diagnosis
We cleaned the engine down and ran it to find the source, the leak was coming from the oil filter housing gasket, the gasket hardened and weeping with oil running down the block from there, not from the valve cover or the crank seals which were dry. That's an oil filter housing gasket replacement, with a fresh gasket and the housing cleaned up, rather than chasing a weep that only spreads.
The work
The oil filter housing was unbolted, the old hardened gasket removed and the mating faces cleaned back to bare metal, and a new genuine Audi-spec gasket fitted with the housing torqued back down to the manual figure. The oil filter was renewed while it was apart, the area cleaned of old oil so any future weep shows up, and the level checked and topped to the correct mark. A road test and a check on the lift confirmed it was dry, with no drips and the level holding.
The outcome
No oil leak, no drips on the driveway, no oil burning off under the bonnet, and the level holding between checks. The Audi went home with the leak sealed. A hardened 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.
