I too notice a little film of dust in the boot. Not enough grit to feel but you can see it when you wipe it with a finger. Always use lots of Bel-ray filter oil. I was worried also and milled out the inside of the cage to get 100% seal. One ride all was OK next ride really dusty and film was back. Like I said not gritty but there none the less. I was using a UNI filter.