If I paid retail, I would only have one extra on hand for each application. When I had been buying Wix for my Cummins for $10/ea., then from Filter1 for just under $5, now getting Purolators from Pep Boys for $1.99 (.99 or .01 with rebate), I am buying all I can get my hands on. Cummins have been running 1/2 million miles and up for years on old technology oil and filters, I don't find any need to improve on that.