Currrent car: 93 Pontiac grand Prix LE, 3.1 V6, 243,000 miles. No problems, mostly Mobil 1 5W30 (and 0W30), few times Pennzoil regular 5W30, and about 30,000 miles of this also on Amsoil 5W30, but mostly (and presently) Mobil 1 5W30. OCI's 7,000 miles.
Before this, an 86 Cadillac Sedan Deville, sold at 265,000 miles and still went over 300,000 miles, Mobil 1 10W30. OCI's 10,000 miles.
Good Day,
Steven