Beth---Be sure that your machine's foot is in the DOWN position when using the auto threader. I have a feeling that is what is making your threader not useable when near the edge of your design.
I throw my used pre-filled bobbins out generally. I do save a few, "in case" I need an extra to refill. However, I cannot comment on whether that is a good idea because I have never had to re-wind a saved bobbin.
As for oiling, I put a reminder on a piece of tape and stuck it to my machine to oil it in the first week of every month----BUT-- the manual suggests this frequency if you use the machine every day, so I adjust the oiling time interval according to how much I estimate I have used the machine in the past month. It is very easy to OVER-OIL the machine and that can cause problems, too. It also is a bit scary where the manual says to turn the machine so the handwheel rests on the table. USe a folded towel on the table when you do that. AND----if you happen to have a USB stick in the machine---REMOVE it BEFORE you move the machine to its side!!!! Otherwise, you could possibly "squish" and break the USB stick and/or the USB port on the machine. BEWARE!!
If your machine is sounding louder or different, I would suggest first a good brushing-out with a soft brush, and a vacuum cleaner attachment if you have one of those miniature ones. Then estimate how much you have actually used your machine in the last month and oil/not oil accordingly.
Hope this is helpful
Kathy Strabel Camas WA