I was amazed the first time I opened my Bernina 801 (bought it used on eBay) how much lint a small space could hold. Lint was felted under and around the feed dogs. A week later, I took a class on machine care and she showed me how to open other areas of the machine and I found even more lint packed in. I dust out at each bobbin change and about every third bobbin, I oil my machine and open everything up to make sure it is lint free.
Packed lint is probably why my Singer sends everything to the left. I plan to give that one a good cleaning before donating it as it is my fourth string machine, so someone else should have a chance to enjoy it.
Cheers, K