RT16 tweeter

The tweeter in one of my RT16s has become crackly. Polk says the OEM part is ab SL6501. I see a nice SL6509 on Ebay. Would that work (other than it doesn't appear to have a bucking magnet on it), or are there other legacy part numbers that would work to expand my options. I saw one post that says Polk has "substitutes" but they didn't mention that when I reached out to them. What is the part number for the substitute if there is such an option? Thanks.