I have a Viking 1+ and always clean the bobbin area before a big project or every month or so. If you google Jan Hennings site "Sew
Much for Retirement" she has some great tutorials for the Vikings. I printed out her instructions and always make sure I get the four screws back in place and indented properly. I also apply two drops of TriFlow on a Q-tip and wipe it over the area before screwing the plate back on.