The gray paste is probably in the transfer ports and crankcase area as well. The gray paste is usually powered aluminum mixed with oil. The powered aluminum is ground up piston skirt from sand, dust or any abrasive that makes it way into the engine. The most common path into the engine is through an improperly serviced air filter. In this case, the pores in the dry filter are probably larger than the dirt particles sailing through the filter pores.
Dry filters require an enormous amount of surface area to have high air flow capability if the pores are small enough to catch ALL of the very fine powder. An outer ware is a waste of money on a dry filter because the pores in the outer ware should be larger than the pores in the dry filtering surface. If the outer ware has smaller pores than the dry filter......there is no need for the dry filter.