I'm not very familier with these engines but I believe fuel can get into the oil via the DPF system.

I assume that the fuel has been leaking into the engine for some period of time

It probably has been. Not wishing to sound harsh but, this fault obviously didn't happen overnight but over a longer timescale as you state, and if you had been checking your oil level on a regular basis it would / should have come to light that the level was rising not falling earlier.

To dilute the engine oil to such an extent that it loses it's ability to sufficiently lubricate would take several weeks, if not longer (unless there was a catastrophic failure in the fuel system which would have been obvious). How often has the oil been changed, and was the correct oil used ? Has the DPF been successfully regenerated when required ? If not, this will cause the system to inject large amounts of fuel in an attempt to regen and if it fails or is aborted by not reaching the required parameters, it will try again and each time, loads of fuel is used which can cause the dilution. If the oil is old or the incorrect grade, the possibility of it losing it's lubricating properties is greater. Just last week I carried out an emergency regen on a 1.6 CR Golf and the instantaneous fuel consumption dropped to just 5.9 MPG ???? Luckily it was also having a service so the oil was changed afterwards which in my opinion, is the best thing to do. If a forced regen is required the car hasn't been driven within the parameters for normal regeneration, and as such, it has tried unsuccessfully at least three times and will weaken the oil.

Good luck with the dealership, I hope it goes well. Just remember to check the oil (and other levels) regularly in future though..............

Edited by The-Mechanic on 24/12/2013 at 07:51