Thanks for that tip. I got a filter same as the one that I pulled out of it. Gasket/o ring appeared undamaged so I used it again. I twice last night tried the tighten slightly/tap procedure you described , but was not successfull. Still leaks. Frustrating. The gasket does not fit snuggly in the groove in the lower half of the filter canister, but I don't have the experience to tell if this is normal. I imagine the next step is to try and find a new gasket. Any suggestions? Bill Make sure you have the right O ring,and the right filter cartridge, if I remember the O ring for the Mack filter is thicker than for a luberfiner. When tightening the clamp, snug it up, then tap all the way around the clamp with a hammer, tighten some more, then tap some more etc. until the clamp is fully seated and the O ring is compressed. Just tightening the clamp without hammering & retightening will not compress the O ring sufficiently. Don't forget to fill the filter housing with oil before starting the engine, and be sure to leave the top plug loose and bleed the air out while the engine is at idle speed. When oil starts escaping around the loose plug, then you can tighten it.