I recently purchased a used 6600 and absolutely love it! I've been through the operators manual, paying attention to the maintenance section. I have taken apart the bobbin area, cleaning it well a couple times. The manual says nothing about oiling anything, but I don't want to mess up this machine by neglecting something I need to be doing. If I need to be oiling it, what kind of oil do I use? Is there anything else that I am missing?