Just pulled the gear case/ from LU to replace impeller on Johnson 6 HP (CD-24). Used outboard I recently bought and gearcase oil was drained for shipment. Noticed a noticeable amount of crud in the gear case unit though the fill hole and looking in from the the top. If there are no leaks should it still be cleaned? Can it be cleaned without the rebuild- ie. w/ a parts cleaner of sorts? Should it be rebuilt? Thanks