If just soaking it dosent get it loose you can drill a hole big enough to get a spray tube in the top side of the case at the bolt hole so you can fill the cavity with penetrant. If that doesn't get it to move you need to cut it out and have a machine shop remove it from the cases. Pretty much going to ruin the swingarm to get it out, but better than ruining the engine cases. There is a steel bushing cast in the case if you make it rotate you will ruin the cases. Trust me I have done this it sucks.