Thanks for the link. But unless I'm not understanding your thread (which is ENTIRELY possible), it still doesn't conclude whether or not to use the smaller O-ring.??This link shows both the Ford and BMW versions, including the O-ring purpose for both.
FGT vs BMW Oil Filter Cap & Cage
In the late 90's and early 2000's some plastics used for Genral Motors hot engine parts deteriorated and crumbled. These problem plastic parts were changed to metal. With this in mind, I thought it might be a good idea to have a spare oil filter cap and cage assembly for my FGT, since, I could...www.fordgtforum.com