Palladium wrote in post #6223383
I'm trying to help the original poster and not trying to confuse him and his situation.
He has an IS lens and need the Mark II extenders to maintain the IS FUNCTIONS. The older version of the extenders will work but IN MY PERSONAL EXPERIENCE he will get better images with the newer Mark II versions of the extenders. I know I did when I upgraded.
Let's add that Canon service does not really service the extenders so I think it's a good idea to use something that at least has a warranty.
To recap when I was in the OP position I upgraded to the new Mark II versions and most photog's would probally do the same.
Peace Out

You were originally trying to persuade the OP to upgrade his 1.4x TC for reasons of "better optics & performance". Now you say it is needed "to maintain the IS FUNCTIONS". I think that your comments can only serve to "confuse him and his situation" 
According to every source of information I have found, the only reason to upgrade is for weather sealing - they are optically identical. Even Canon don't claim to have improved the optics. The Mk II has new anti-reflective coatings, but I've not yet seen anyone claim that this makes a difference. The TC has no effect on IS! Perhaps your old Mk1 converter was faulty?