My DH does black powder shooting and makes his own clothing and gear for reacting. I keep my Viking 6020 especially for him. They are a great, tough machine, the only one I know that has a true low gear for tough sewing.
Finding someone who knows this series of machines is difficult and many shops will tell you it's not fixable because they don't know how to work on them. I am lucky to have found an older Viking guru about an hour from me. I have had 3 rebuilt and currently have 2 of them, the 3rd lives with my sister-in-law. Added to what was said above about the self-oiling getting hard, they also have couple of parts that are a weakness, the internal cam and the take up slide (they crack, but parts are available). My guru usually charges $200 for a complete rebuild plus parts. The most recent time, my friend wanted to gets hers worked on and I took mine (found at a thrift shop for $10) along, thinking to offer it to him for parts because it was frozen. He convinced me it was worth saving and gave us a "two-fer" and now that "runs like new" machine is going to go to another friend. Unfortunately I am in Oregon!
There is a yahoo group called "vikingsewingmachinespre1980" run by a retired viking guru, and he would probably be able to tell you where to start to diagnose your issue. He also has a lot of viking technical info in the files section, and he maintains a listed of trusted techs who work on the older vikings. That is how I found my guy.
Last edited by Skyangel; 05-14-2017 at 08:01 PM.