If there is a crack in the housing, the only answer is a replacement housing.
But I doubt that is the case, mine were doing that (not as bad, but Im in Texas north of the "dry line"). The cure was to switch to the Mopar vented, filtered "stoppers". That way, the housing can breathe without dust getting in.

Of course, those kits are no longer available. There is a thread here SOMEWHERE, where an owner cut holes in the non-vented stoppers and glued in little patches of fiberglass furnace filter.

If you can't SEE the crack, there is no crack - that is my opinion, for what it's worth.