Yes, this sounds like it could be a valve cover gasket problem. You might also want to check the volute of your turbo. If your output shaft seal has failed it would leak oil into the volute, compress it, and force feed into your engine, but it would be on all your spark plugs, so yes, back to the valve cover gasket. I have included a link for you to go to down below:
Please go through this guide and get back to us with what you are able to find out please.
Saturday, April 13th, 2019 AT 4:47 PM