Ruserious ; the engines are not overserviced, they are filled to a full mark on the sightglass which is on the side of the oil tank. If a bit is spilled during servicing, usually with the poor hapless mecahnic hanging on to a pair of rickety steps, then it will drain down the scupper drain and out the mast. The breather will always make a mess of any Trent engine.
Warlock ; Ask yourself who makes a mess in the flight deck and would you be prepared to clean up after someone else ?