Paul,
If the blade is tracking on the center of the tires, I don't see where you've got a problem. Just put in a new insert, and be happy with the saw.
The hole for the insert might be machined a bit off center, but I doubt it. My 30+ year old 14" saw does the same thing - the blade is about ¼" forward of center in the insert. I never really noticed it until now, when I looked at it after reading your post, and seeing your picture. The saw works just fine - tracks well, cuts well, runs quietly - so I don't see a problem.
If yours is tracking well, and cutting well, just make a new insert, but don't cut the blade slot all the way back, and use the saw. No problem!