Originally Posted by ksisler

As others have said, it is not a huge amount of "offness". Easier though to just measure the gap between the DT and the backside of each arm... It could be that the left arm is bent a bit also. Pretty common, so look for that possiblitity. Replacment left arms are cheap...so if bent, post all the specifics and pictures and we can give you a URL to the right part ($9-$20 typically).

After reading everything posted, post anew if this is something you really want to pursue a fix for. From the original postings, fixing it yourself will not be likely as there are specific skills and tools need. A good bike shop could do. It will cost you a bit less than $100 or so for parts and labor.