Mine was failing exactly like Kev describes. It's a common failure on these sump pans. I have a picture but cant seem to upload it on here and of course photobucket is no longer an option.
Yep...no sign of oil around the sides of the pan and a thick scabby lump of rust on the bottom of the pan that oil is dripping from. Was a surprise to me that such a thing could happen, especially since it is protected from the elements by the undertray. I presume (worryingly) that this is a drop of water sitting inside the pan under the oil that leads to corrosion.
I'll get a picture when I do the swap
It think it happens because small amounts of water moisture can get into the oil. When you switch off, it sinks to the bottom of the sump as it's heavier than the oil. As the water can have contaminants that make it acidic, it has a tendency to erode the steel at the point at which it collects, or wherever there is a scratch or dent maybe.
The best thing to do is to try and do longer runs and get the engine/oil hot to try and turn any condensed water back into steam and drive it out. Lots of cold/short drives tend to cause this problem.
Edited by Nev, 09 January 2018 - 11:24 PM.