I had a 6340 and took it to a local serviceman -- he had no clue and apparently did not want to bother learning -- he suggested I scrap it -- it was over 40 years old and I could not find anyplace in Kentucky to get it serviced. Result -- I let him scrap it, but kept all the cams, attachments and booklets.
Found a Yahoo Group that guides you through working on it yourself. Result -- I have since bought two vintage vikings off of e-bay. I loved that machine. Had I known in 2009, what I know now, it would never have been scrapped. On the upside, I did purchase my 301a from that serviceman to replace it, and I love that machine as well, and will work on it myself thanks to another Yahoo Group on Vintage Singers.