I just cut open a Castrol, Penske, and a Wix. The Castrol and Penske were from Kmart, the Wix from a local parts store. I don't have the filter numbers in front of me, but, the Castrol and penske filters were xx3600's, and the Wix was a 51516.
The Cast, and Pen I cut open were deninitely made by...