15W-50 is a good oil. It got really popular during the O-320H skyhawk days because it has the antiwear additive called out for by an AD on the "H" motors. Otherwise you had to add the Lyc antiwear stuff to your oil. Aeroshell W100 plus now has the same additive. Personally, I still like straight W100 unless cold starts are necessary. I've broken down Navajo TIO 540's with 2000 hours of W100 time and found sweat fingerprints still on the bearing journals. 15W-50 is generally acknowledged to exacerbate small leaks compared to a straight oil and it costs more. In the shops we used to call it "black gold". As an aside, when checking oil filters for metal we used to call that "panning for gold". If you found metal, the shop made money.
