So to re visit this one more time, the Napa filter 1001 is the perfect fit for the canister, however the gasket is not. One is to small, the other is to large, unless the wrong gasket is in the box. The gasket for the 1121 filter is the correct fit.
Sometimes they have alternate gaskets as a separate part number for oil filters at NAPA and I presume other places.
I don't think it was the case with my GMC but another recent application for a NAPA canister filter did come with the wrong gasket (for my application) and after looking in the catalog the correct gasket was listed and even a third optional gasket. If only we had checked for that info when ordering the filter the first time it would have saved a trip or two.
I'm going to try the gasket that came with the 1121 filter as it seems to fit the lid correctly, so long as it seals. If that's the case I'll be able to order a few of the Wix 15086 gaskets, and can order the 1001 filters or 51001 Wix filters.
