Hmmm. it's possible you have a pocket in your head that is holding oil. you might wanna get the valve cover off, it's not too difficult, and look inside for a blockage of some type. I'll check my parts car, and see what I see in there that could be holding oil. the increasing part is worrisome, it could indeed be fuel mixing with the oil. but I would not think it would burn off, diesel and motor oil are very similar, and the control rings would act the same with either.