Panamera 4S Aircon Smell

[S70JPS]

For a couple of days now my Panamera 4S 2012 aircon has been smelling of old engine oil. It is intermittent through the vents and only seems to happen when the air is being heated. There are no signs of an oil leak or any dislodged pipes in the engine bay. I did have a lot of work done just over a year ago to fix a minor oil leak but was assured everything had been cleaned off and it looks as though it has. However if it was from this I would have expected to have had the smell last winter. I'm only using the car for very short journeys at the moment 2-4 miles and not sure if that has any bearing on the problem? Have any other owners experienced the same and if so what was the cause? It has already had the aircon fire risk recall done. I would like to ask on here before I dig deep at the OPC.