I choose to bring it back to Indiana. Read the story in this post
I did not saw the repair on my unit but there was another Sanibel 3500 with the same problem when I visited the repair facility. The cap was already removed and Ronald showed me where the frame was reinforced.
I decided to go with the Trailair king pin after talking with Ronald Green. I installed it my self at home before I went back to get my Sanibel.
Now, I always check to see if I am going to see some flexing when I hitch-up my fifth wheel but so far, so good. no flexing at all. There is also a plus here that I did not mention. I always had problem locking the entrance door. Sometime, the deadbolt would stick half way. now everything is fine. I guess it re-aligned the whole frame.
Hope it helps