The No Toil kit comes with it's own biodegradable "grease". I don't know about the filters sealing against the air box by themselves, might be true, but even when I used regular air filter oil for the filter, and gas to clean the filter, I used a waterproof grease as a sealer. It may not be necessary, just something I was told somewhere so I've always done it that way. Might need some more input here from someone else to see what they do. When I clean my filter, I use warm water and the cleaner that comes with the kit, after I'm done the water always looks dirty so I know the filter is trapping dirt, I just don't know what, if anything, is getting through.