Hello new user with Gruen question

I hope this is the right place to post this. I looked for a Gruen section but I guess it doesn’t exist. I have a 710rss that I purchased and am trying to source a crystal for. But everywhere I’ve looked I can’t find a part number related to the watch type. In doing research I’ve come across 2 potential names “champ” or “nautilus “ but nether those nor the number show up on any of the cross ref charts I have found. I would appreciate the help!