Older Pm9 different from the newer PM9 problem

I bought a new recoil guide assembly from older (#VA****) Kahr and discovered the circular flat part that fits against the barrel lug is different. I called Kahr ask about the difference and they sent me another assembly and it's the new assembly as well. Can I use the new one or do I have to buy a new barrel?

The new is on the left, and my old assembly is on the right. Are the old and new lugs cut differently???

http://i195.photobucket.com/albums/z...DSC04789-1.jpg

On the old model I have, once I bought the new barrel and recoil rod/spring set up I then had to send it back to Khar to have the frame milled to fit both properly