580321 is the P/N for the Evinrudes condensers, available from your friendly neighbourhood OMC/BRP dealer. It’s the top one in the photo. Not sure about the Mercs.
Hey James, I found the table for Merc condensers and it shows you need a cap with a rating of .15-.19 uF for your mag. If you can’t find an original, Digi-Key has modern film caps which can be adapted to outboard magneto systems.