Likewise on the CA351. Used round 1/2" foam insulation rope and contact cement to grove in top of filter for a gasket and left air box cover o-ring in place. The air box cover pressed nicely into the foam and I could clearly see the indentation each time I replaced the filter. Renewed the foam rope with each filter change.
Jim
I used the CA351 for many years without issue until last year. Went to Colorado and when I was above 7000 feet it ran terrible and couldn't get above 40mph. Replaced it with a K&N.