Hi, I was given a viking from 1973/4 which had a stuck-in reverse button.
I found and joined a yahoo group for pre 1980 viking machines and asked for advice which was so helpful. I managed to loosen off the button and it now sews so well. I used a spray similar to WD40 but with a silicone ingredient which was recommended. I live in the UK and sourced my spray through a carparts shop. I downloaded a service manual from the yahoo group which I`ve got for future reference too. Hope this can help