Mine is on the top of the axle, RH side outboard edge just inboard of the spring on a 2010 duratec car. It has a sort of loose plastic cap. They are usually blocked by the application of the rust proofing wax. People who know this even when applying it and give the cap a jiggle haven't allowed for the wax setting around the base!
The seals fail in the axle because as the axle heats up in use the oil expands and under that pressure it can be forced past the outboard axle seals. luckily a Morgan doesn't suffer with sudden cooling creating a vacuum within the axle like a land rover entering water which results in water being sucked into the axle casing with the resulting oil contamination.
