top_driver, I'm guessing that it's brake fluid that's leaked into the brake servo, if it is then you will have to remove the servo and clean it out. Don't forget brake fluid is pretty oily and it will leave a residue unless cleaned out properly.
good things do happen. i had car running and pressed brake repeatedly. after plenty misfire it stopped. the leak was caused by changing brakes and forgetting to open reservoir cap.
You can clean out your brake fluid leak residue with brake Cleaner which should dry it out quickly. Mind you brake fluid left uncleaned will strip off the paint and corrode the panels.
You have not "lost" 2 litres of engine oil, most of it is in the oil filter housing.
Most manufacturers give 2. Oil change capacities a lower figure without oil filter change and a high figure with the oil filter change.
Unless of course your engine was losing oil before this oil change.