After I took the D4 for an oil change (as per rebuild warranty requirements) I noticed it was showing as over filled.
I had to take it to them for a start-motor refurb so I asked them to check the oil; they said it wasn't very much over and not to worry about it.
Now it's got a significant oil leak! Are the two likely to be related?

Until you know where the leak is from it will be impossible to say.

It was a holed turbo oil return hose. Could have been nasty! Glad I didn't drive it much.