I bought an inexpensive computerized Singer several years ago. When doing maintenance once, I found what I thought was lint way down under the bobbin case. I got tweezers to pull it out--it was some kind of lubricant-soaked wadding stuck in there. Researching online, I found out it was not supposed to be removed, but no help at all on what to do if it was removed in error. Even Singer was no help.
I stuck it back in as well as I could, and it sewed just fine. Still does.