I wrote the lower non-rebuildable section of the shock might be bad allowing the spongy movement. could be the problem.
I wondered about that. The only rebuild kit I could find was a pack with two seals. No info on the section that held the spring or damper/piston. They are discontinued by Progressive Suspensions and don't seem to have any technical data available to anyone who still has them. The 416s are also used on Harleys and they seem to swear that they use way more oil than the Goldwing people are talking. They also come in 11", 12" and 13" give or take some fractions. I wonder if this has anything to do with the amount of oil.