If you are going to work on your bike, you need two things, a Clymer's manual and a thread file. You can pick one up from MSC (www.mscdirect.com) for less than 13 bucks and has files to fix 0.80mm, 1.00mm, 1.25mm, 1.50mm, 1.75mm, 2.00mm, 2.5mm, and 3.0mm pitch threads. This should fix your problem as long as the threads have not been hardened which I am guessing they are not if they are boogered. If this doesn't work, then you can always do what others have suggested, weld it on and replace at next teardown.
MSC part number for a metric thread file is 05007034.