All GDIs are having this problem, more or less. It's a design feature ! Why don't you install an OCC (Oil Cath Can)?
I don't have a direct injection car. I am just curious. Looking on Youtube there are countless clips showing carbon deposits, sludge etc. in GDI cars.
I hear that some brand designs are worse than others (VW, Audi etc) for this and that Toyota (at least) has another injection site as well as the the injector in the combustion chamber in their cars....to reduce deposits.
Just wondered if Hyundai is currently/recently doing anything similar and also wondering how bad a problem it REALLY is in Hyundais.
As a complete novice but weekend warrior home mechanic, I can't fathom why this design 'feature' still exists.