My car always had 5W-40 synthetic. 94k miles, dealer maintained, bought it 9 months ago from the original owner. It had a very slight, barely noticable wetness around the headgasket and the oil pan. I noticed that the 20k miles i travelled with it during less than a year made it worse. During confinement my car was parked uphill for 2 months with very little use and i think it made everything worse, including what looks like a rear main seal leak. I wonder what made the leaks worse. Is it my heavy use of a car that spent it's life garaged and travelled something like 3/5k miles each year ? Last oil change i switched to Shell HX7 10W-40 semi-synthetic. Do you think that it will slow the leaks ? Should i even switch to something like 15W-40 dino or 10W-50? This car is used 60% highway, 30% country roads, 10% short trips and city driving.