Hi GM. I'm in forward progress. I got my first 421 and a 416 recone kit in hand. I stripped the 421 and cleaned it. This unit has two screens. One on the magnet rear, and one under the dust cap. The one under the dust cap has what appears to be metal spatter; not so as to completely block it off, but there is some. It doesn't come off when I dab it with adhesive tape or shoot it with compressed air. Should I leave it in place? Do you have a recommendation for how to block off the back vent?

Thanks.
Les