I bough mine before reading about the broken #6 valve problem. Not a clear answer as to why nor what to do about stopping it from happening. Too soon to say the new and improved parts will solve the problem or the new engine. Why is this happening mainly in MHs and hopefully only in the 600-650 HP engines?
I was able to get a camera to the #6 intake and it didn’t look any different than the 4 or 5. I am using the “Ugly Fix” and I installed a metal freeze plug in the EGR tube at 46K miles and it now has 56K. At this point all I can do is cross my fingers and hope for the best as we really like this MH.
*OP, NO WAY would I buy a ISX, especially a 600-650 HP. I would keep what you have until a definite cause and cure is guaranteed...not there yet.