i don't believe it is an issue of improper fit. the gaskets in a c3p 'fit' perfectly.
it's just making them defiy gravity and stay in the top of the cap while you slip it on that the grease helps with.
i've used the more spendy napa 1010 and it's rubber gasket fits no better than the 4$ fram filter. mind you this has been a couple years as i have not use dmy 8n since 09, thus it has not been serviced since then.