I can remember when I was an apprentice removing the sumps from some cars and it looked like someone had thrown sulphur in them. The sump pan was yellow from all the sulphur and the bearing and rings look like they had been sand blasted. I have never used Castrol oils since. It ironic that Castrol GTX 2 was actually supplied to them by shell. Castrol GTX 2 was shells entry level oil (not a bad oil) but marketed by Castrol as a premium oil. I didn't find this out until 15 years later.