Yeah I accidentally poured 4 quarts of synth during an oil change before I noticed, and it slowly leaked out the rear seal. I let it run it course and added 1 quart of cheap gas station oil a week, its since stopped. My seals are 23 years old, theres not way they can handle this thin/slick stuff. Maybe if I had new seals I would.Is that from personal experience? Because I've had no issues with leaking seals on mine.