After many years working on aircraft, and servicing aircraft engines with synthetic oil. In 1962 I put the first synthetic oil in a 1958 Oldsmobile Holiday 98, the car had about 50k on it when I changes over. I ran the car for several years, and it had well over 100k on it when I went to Viet Nam and sold it to a friend. He continued to use the oil, and put several thousand more miles on the old car before it was sent to an early grave as a result of a wreck. We were running the same oil used in the jets, it was a 10w oil, the lifters were a little noisy when first started, but that was also common on a high mileage car running petroleum based oil, the old car never spotted, or leaked oil.
I didn't run a synthetic oil again until 1977. After returning from Europe, I purchased a new Ford, F-250 with the 460 engine. When the warranty ran out, I switched over to Mobil 1, I worked that truck hard, it had over 130k on it when I finally traded, never an engine problem or leak problem. I later bought a Toyota pick up, I don't remember when, but I switched it over to Mobil 1 after the warranty ran out on it. When I was forced off the road and rolled five times the truck had over 230k. It never had a bolt turned on the engine except for valve adjustments. In addition, I ran the Mobil 1 in my sons truck, both daughters Toyota's, and my wife's Cadillac, they averaged about 5-6k between oil changes. I could run the Toyota pickup 6000 miles, pull the dip stick and the oil still looked fresh.
For the past few years I have been running a diesel, I use Shell Rotella T in it.