Our local O'Reilly's' carries a 2 1/2 gallon jug of Mystic 15-50 syn blend with a REAL high zinc content that I've been using & have had real good service with. I buy the 3 to 5 pack of economy filters, they're usually missing a couple of O-rings so I hang on to my old ones until I know what I need. Seems with the Iron Barrels & the UCE filters, I have the same issue.